Charles Rice - Academia.edu (original) (raw)

Papers by Charles Rice

Research paper thumbnail of The altered vestibular-evoked myogenic and whole-body postural responses in old men during standing

Experimental Gerontology, 2014

Age-related decrements within the sensorimotor system may lead to alterations and impairments in ... more Age-related decrements within the sensorimotor system may lead to alterations and impairments in postural control, but a link to a vestibular mechanism is unclear. The purpose of the present study was to determine whether vestibular control of standing balance is altered with adult aging. Eight old (~77 years) and eight young (~26 years) men stood without aids on a commercially available force plate with their head turned to the right, arms relaxed at their sides and eyes closed while receiving stochastic vestibular stimuli (0-25 Hz, root mean square amplitude=0.85 mA). Surface electromyography signals were sampled from the left soleus, medial gastrocnemius and tibialis anterior. Whole-body balance, as measured by the anteroposterior forces and muscle responses, was quantified using frequency (coherence and gain functions) and time (cumulant density function) domain correlations with the vestibular stimuli. Old men exhibited a compressed frequency response of the vestibular reflex with a greater relative gain at lower frequencies for the plantar flexors and anteroposterior forces than young. In the time domain, the peak amplitude of the short latency response was 45-64% lower for the plantar flexors and anteroposterior forces (p≤0.05) in the old than young, but not for the tibialis anterior (p=0.21). The old men had a 190% and 31% larger medium latency response for only the tibialis anterior and anteroposterior forces, respectively, than young (p≤0.01). A strong correlation between the tibialis anterior and the force response was also detected (r=0.80, p<0.01). In conclusion, net vestibular-evoked muscle responses led to smaller short and larger medium latency peak amplitudes in anteroposterior forces for the old. The present results likely resulted from a compressed and lower operational frequency range of the vestibular reflexes and the activation of additional muscles (tibialis anterior) to maintain standing balance.

Research paper thumbnail of Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology

To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular ... more To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P<0.05). NF jiggle was significantly higher in the TA compared to VM (P<0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P<0.05). For VM, NF jiggle was positively correlated ...

Research paper thumbnail of Increased neuromuscular transmission instability and motor unit remodelling with diabetic neuropathy as assessed using novel near fibre motor unit potential parameters

Clinical Neurophysiology, 2014

To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in... more To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in patients with diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG) and near fibre (NF) motor unit potential (MUP) parameters. The tibialis anterior (TA) muscle was tested in 12 patients with DPN (65 ± 15 years) and 12 controls (63 ± 15 years). DQEMG was used to analyze electromyographic (EMG) signals collected during voluntary contractions. MUP and NF MUP parameters were analyzed. NF MUPs were obtained by high-pass filtering MUP template waveforms, which isolates contributions of fibres that are close to the needle detection surface. NF MUP parameters provided assessment of motor unit size (NF area), fibre density (NF fibre count) and contribution dispersion (NF dispersion) and neuromuscular transmission instability (NF jiggle). DPN patients had larger (+45% NF area), more complex (+30% NF fibre count), and less stable (+30% NF jiggle) NF MUPs (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). No significant relationships were found between NF MUP stability and denervation, or strength; however NF MUP complexity was positively related to TA denervation in the DPN group (r=0.63; p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). NF MUP complexity and instability were positively related in DPN patients (r=0.46; p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). DPN is associated with neuromuscular transmission instability and MU remodelling that can be assessed using DQEMG. DQEMG-derived NF MUP parameters may be useful in identifying patients in early stages of neuromuscular dysfunction related to DPN.

Research paper thumbnail of Velocity dependence of eccentric strength in young and old men: the need for speed!

Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme, Jan 3, 2015

Older adults better maintain eccentric strength relative to isometric strength, as indicated by a... more Older adults better maintain eccentric strength relative to isometric strength, as indicated by a higher ratio of eccentric:isometric torque as compared with younger adults. The effect of increasing angular velocities (>200°/s) on the age-related maintenance of eccentric strength has not been tested and thus it is unknown whether the eccentric:isometric ratio is velocity dependent in old age. The purpose of this study was to investigate eccentric strength of the ankle dorsiflexors over a large range of lengthening angular velocities in young and older men. Isometric neuromuscular properties were assessed on a HUMAC NORM dynamometer. Nine young (∼24 years) and 9 older (∼76 years) healthy men performed maximal voluntary eccentric contractions at angular velocities of 15-360°/s. Despite near full voluntary activation (>95%), the older men were ∼30% weaker than the young men for isometric strength (P < 0.05). Across all lengthening velocities, older men had a greater eccentric:...

Research paper thumbnail of Decreased muscle endurance associated with diabetic neuropathy may be attributed partially to neuromuscular transmission failure

Journal of Applied Physiology, 2015

Diabetic polyneuropathy (DPN) can cause muscle atrophy, weakness, contractile slowing and neuromu... more Diabetic polyneuropathy (DPN) can cause muscle atrophy, weakness, contractile slowing and neuromuscular transmission instability. Our objective was to assess the response of the impaired neuromuscular system of DPN in humans when stressed with a sustained maximal voluntary contraction (MVC). Baseline MVC and evoked dorsiflexor contractile properties were assessed in DPN patients (n=10) and controls (n=10). Surface electromyography (EMG) was used to record tibialis anterior evoked maximal compound muscle action potentials (CMAPs) and neuromuscular activity during MVCs. Participants performed a sustained isometric dorsiflexion MVC for which task termination was determined by the inability to sustain &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;60% MVC torque. The fatigue protocol was immediately followed by a maximal twitch, with additional maximal twitches and MVCs assessed at 30 seconds and 2 minutes post-fatigue. DPN patients fatigued ~21% more quickly than controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) and featured less relative EMG activity during the first third of the fatigue protocol compared to controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). Immediately following fatigue, maximal twitch torque was reduced similarly (~20%) in both groups and concurrently CMAPs were reduced (~12%) in DPN patients, whereas they were unaffected in controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). Twitch torque and CMAP amplitude recovered to baseline 30-seconds post-fatigue. Additionally, at 30-seconds post-fatigue, both groups had similar (~10%) reductions in MVC torque relative to baseline, and MVC strength recovered by 2-minutes post-fatigue. We conclude DPN patients possess less endurance than controls, and neuromuscular transmission failure may contribute to this greater fatigability.

Research paper thumbnail of Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

Clinical Neurophysiology, 2015

To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular ... more To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). NF jiggle was significantly higher in the TA compared to VM (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). For VM, NF jiggle was positively correlated with NF count and MUP area (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05), and no significant correlations were found between NF jiggle and S-MUP amplitude, MUP duration, or MUP peak-to-peak voltage (MUNE was not calculated for VM, so no correlation could be made). Healthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. NF jiggle derived from DQEMG can be a useful method of identifying impairment with neuromuscular dysfunction at various stages of MU remodeling and aging.

Research paper thumbnail of Increased neuromuscular transmission instability and motor unit remodelling with diabetic neuropathy as assessed using novel near fibre motor unit potential parameters

Clinical Neurophysiology

Objective To assess the degree of neuromuscular transmission variability and motor unit (MU) remo... more Objective To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in patients with diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG) and near fibre (NF) motor unit potential (MUP) parameters. Methods The tibialis anterior (TA) muscle was tested in 12 patients with DPN (65±15 yrs) and 12 controls (63±15 yrs). DQEMG was used to analyze electromyographic (EMG) signals collected during voluntary contractions. MUP and NF MUP parameters were analyzed. NF MUPs were obtained by high-pass filtering MUP template waveforms, which isolates contributions of fibres that are close to the needle detection surface. NF MUP parameters provided assessment of motor unit size (NF area), fibre density (NF fibre count) and contribution dispersion (NF dispersion) and neuromuscular transmission instability (NF jiggle). Results DPN patients had larger (+45% NF area), more complex (+30% NF fibre count), and less stable (+30% NF ...

Research paper thumbnail of Shortening-induced torque depression in old men: implications for age-related power loss

Experimental gerontology, 2014

Following active muscle shortening, the steady-state isometric torque at the final muscle length ... more Following active muscle shortening, the steady-state isometric torque at the final muscle length is lower than the steady-state torque obtained for a purely isometric contraction at that same final muscle length. This well-documented property of skeletal muscle is termed shortening-induced torque depression (TD). Despite many investigations into the mechanisms of weakness and power loss in old age, the influence of muscle shortening on the history dependence of isometric torque production remains to be elucidated. Thus, it is unclear whether older adults are disadvantaged for torque and power production following a dynamic shortening contraction. The purpose of this study was to evaluate shortening-induced TD in older adults, and to determine whether shortening-induced TD is related to power loss. Maximal voluntary isometric dorsiflexion contractions (MVC; 10s) in 8 young (25.5±3.7years) and 9 old (76.1±5.4years) men were performed on a HUMAC NORM dynamometer as a reference, and the...

Research paper thumbnail of Decay of force transients following active stretch is slower in older than young men: support for a structural mechanism contributing to residual force enhancement in old age

Journal of biomechanics, Jan 17, 2014

Following active lengthening of muscle, force reaches an isometric steady state above that which ... more Following active lengthening of muscle, force reaches an isometric steady state above that which would be achieved for a purely isometric contraction at the same muscle length. This fundamental property of muscle, termed "residual force enhancement (RFE)," cannot be predicted by the force-length relationship, and is unexplained by the cross-bridge theory of muscle contraction. Recently, we showed that older adults experience higher RFE than young for the ankle dorsiflexors primarily owing to a greater reliance on passive force enhancement (PFE) and similar RFE for the knee extensors but a greater contribution of PFE to total RFE. Natural adult aging may prove a useful model in exploring mechanisms of RFE which may reside in the dissipation of force transients following stretch. A post-hoc analysis was conducted on previously described RFE experiments in young (~26 years) and old (~77 years) men for the dorsiflexors and knee extensors to fit the force following stretch with...

Research paper thumbnail of The relationship between blood pressure and sciatic nerve blood flow velocity in rats with insulin-treated experimental diabetes

Diabetes & vascular disease research : official journal of the International Society of Diabetes and Vascular Disease, Jan 22, 2014

Peripheral nerve blood flow (NBF) does not autoregulate but, instead, responds passively to chang... more Peripheral nerve blood flow (NBF) does not autoregulate but, instead, responds passively to changes in mean arterial pressure (MAP). How this relationship is impacted by insulin-treated experimental diabetes (ITED) is unknown. We tested the hypothesis that ITED will reduce NBF across a range of MAP in Sprague Dawley rats. Following 10 weeks of control or ITED conditions, conscious MAP (tail-cuff) was measured, and under anaesthesia, the MAP (carotid artery catheter, pressure transducer) and NBF (Doppler ultrasound, 40 MHz) responses to sodium nitroprusside (60 µg/kg) and phenylephrine (12 µg/kg) infusion were recorded (regression equations for MAP vs NBF were created for each rodent). Thereafter, motor nerve conduction velocity (MNCV) and nerve vascularization (haematoxylin and eosin stain) were determined. Conscious MAP was higher and MNCV was lower in the ITED group (p < 0.01). In response to drug infusions, the ΔMAP and ΔNBF were similar between groups (p ≥ 0.18). Estimated co...

Research paper thumbnail of The effect of knee joint angle on plantar flexor power in young and old men

Experimental Gerontology, 2014

Human adult aging is associated with a loss of strength, contractile velocity and hence, power. T... more Human adult aging is associated with a loss of strength, contractile velocity and hence, power. The principal plantar flexors, consisting of the bi-articular gastrocnemeii and the mono-articular soleus, appear to be affected differently by the aging process. However, the age-related effect of knee joint angle on the torque-angular velocity relationship and power production of this functionally important muscle group is unknown. The purpose was to determine whether flexing the knee, thereby reducing the gastrocnemius contribution to plantar flexion, would exacerbate the age-related decrements in plantar flexion power, or shift the torque-angular velocity relationship differently in older compared with young men. Neuromuscular properties were recorded from 10 young (~25 y) and 10 old (~78 y) men with the knee extended (170°) and flexed (90°), in a randomized order. Participants performed maximal voluntary isometric contractions (MVCs), followed by maximal velocity-dependent shortening contractions at pre-set loads, ranging from 15 to 75% MVC. The young men were~20-25% stronger, 12% faster and~30% more powerful than the old for both knee angles (P b 0.05). In both age groups, isometric MVC torque was~17% greater in the extended than flexed knee position, with no differences in voluntary activation (N95%). The young men produced 7-12% faster angular velocities in the extended knee position for loads ≤30% MVC, but no differences at higher loads; whereas there were no detectable differences in angular velocity between knee positions in the old across all relative loads. For both knee angles, young men produced peak power at 43.3 ± 9.0% MVC, whereas the old men produced peak power at 54.8 ± 7.9% MVC. These data indicate that the young, who have faster contracting muscles compared with the old, can rely more on velocity than torque for generating maximal power.

Research paper thumbnail of Torque loss induced by repetitive maximal eccentric contractions is marginally influenced by work-to-rest ratio

European Journal of Applied Physiology, 2004

The influence of different work-to-rest (W:R) ratios during fatigue induced by maximal eccentric ... more The influence of different work-to-rest (W:R) ratios during fatigue induced by maximal eccentric contractions is unknown. The present study sought to expand the understanding of the task-dependent nature of eccentric contractions, and the associated fatigue, during exercise and acute as well as extended recovery periods. Using a Biodex multi-joint dynamometer, the ankle dorsiflexors of eight men [26 (4) years] were fatigued with 150 maximal eccentric contractions. Set structure was manipulated such that one leg performed 3 sets of 50 repetitions (short rest protocol, SRP), and the other leg performed 15 sets of 10 repetitions (long rest protocol, LRP). A 1-min rest interval separated each set, which resulted in 2 and 14 min of total rest for the SRP and the LRP, respectively. At fatigue, the SRP demonstrated a marginally greater loss of average peak eccentric torque than the LRP (P<0.05). In the acute period following fatigue, isometric peak torque loss and the degree of lowfrequency fatigue (LFF) were not recovered (P<0.05) and were equivalent for both protocols. Significant impairment of both eccentric and isometric torque was persistent and equal for each protocol at 96 h of recovery (P<0.05). These findings suggest that the W:R ratio has a modest influence on the fatigue (torque loss) induced by maximal eccentric contractions, but maximal isometric torque during recovery and LFF are insensitive to changes in total rest time.

Research paper thumbnail of Length dependent loss of motor axons and altered motor unit properties in human diabetic polyneuropathy

Clinical Neurophysiology, 2014

Patients with diabetic polyneuropathy (DPN) have fewer motor units in a lower (tibialis anterior ... more Patients with diabetic polyneuropathy (DPN) have fewer motor units in a lower (tibialis anterior [TA]) and upper limb (first dorsal interosseous [FDI]) muscle compared to age-matched controls. Neuromuscular properties of TA are more severely affected in DPN than FDI as demonstrated by the degree of motor unit loss, and increased MUP complexity. DQEMG-derived MUNE may provide a more sensitive or useful complementary measure of early involvement of the motor system in DPN versus results of standard motor nerve conduction studies.

Research paper thumbnail of Exercise Training Enhances Insulin-Stimulated Nerve Arterial Vasodilation in Rats with Insulin-Treated Experimental Diabetes

AJP: Regulatory, Integrative and Comparative Physiology, 2014

Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechani... more Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechanism. Experimental diabetes reduces vasa nervorum NO reactivity. Studies investigating hyperglycemia and nerve arterial vasodilation typically omit insulin treatment and use sedentary rats resulting in severe hyperglycemia. We tested the hypotheses that 1) insulin-treated experimental diabetes and inactivity (DS rats) will attenuate insulin-mediated nerve arterial vasodilation, and 2) deficits in vasodilation in DS rats will be overcome by concurrent exercise training (DX rats; 75-85% VO2 max, 1 h/day, 5 days/wk, for 10 wk). The baseline index of vascular conductance values (VCi = nerve blood flow velocity/mean arterial blood pressure) were similar (P ≥ 0.68), but peak VCi and the area under the curve (AUCi) for the VCi during a euglycemic hyperinsulinemic clamp (EHC; 10 mU·kg(-1)·min(-1)) were lower in DS rats versus control sedentary (CS) rats and DX rats (P ≤ 0.01). Motor nerve conduction velocity (MNCV) was lower in DS rats versus CS rats and DX rats (P ≤ 0.01). When compared with DS rats, DX rats expressed greater nerve endothelial NOS (eNOS) protein content (P = 0.04). In a separate analysis, we examined the impact of diabetes in exercise-trained rats alone. When compared with exercise-trained control rats (CX), DX rats had a lower AUCi during the EHC, lower MNCV values, and lower sciatic nerve eNOS protein content (P ≤ 0.03). Therefore, vasa nervorum and motor nerve function are impaired in DS rats. Such deficits in rats with diabetes can be overcome by concurrent exercise training. However, in exercise-trained rats (CX and DX groups), moderate hyperglycemia lowers vasa nervorum and nerve function.

Research paper thumbnail of Motor Unit Survival in Lifelong Runners Is Muscle Dependent

Medicine & Science in Sports & Exercise, 2012

A contributing factor to the loss of muscle mass and strength with adultaging is the reduction in... more A contributing factor to the loss of muscle mass and strength with adultaging is the reduction in the number of functioning motor units (MUs). Recently, we reportedthat life-long competitive runners (masters runners; ~66y) had greater numbers of MUs in a leg muscle (tibialis anterior) than age-matched recreationally active controls. This suggested that chronic exposure to high levels of physical activity may limit the loss of MU numbers with adultaging. However, it is unknown if this finding is the result of chronic activation of the specificallyexercised motoneuron (MN) pool (i.e., tibialis anterior), or an overall systemic neuroprotective effect of high levels of physical activity. Purpose: The purposewas to estimate the number of functioning MUs (MUNEs) in the bicepsbrachii (an upper body muscle not directly loaded by running) of 9 young (27±5y) and 9 old (70±5y) men, and 9 life-long competitive masters runners (67±4y).

Research paper thumbnail of The altered vestibular-evoked myogenic and whole-body postural responses in old men during standing

Experimental Gerontology, 2014

Age-related decrements within the sensorimotor system may lead to alterations and impairments in ... more Age-related decrements within the sensorimotor system may lead to alterations and impairments in postural control, but a link to a vestibular mechanism is unclear. The purpose of the present study was to determine whether vestibular control of standing balance is altered with adult aging. Eight old (~77 years) and eight young (~26 years) men stood without aids on a commercially available force plate with their head turned to the right, arms relaxed at their sides and eyes closed while receiving stochastic vestibular stimuli (0-25 Hz, root mean square amplitude=0.85 mA). Surface electromyography signals were sampled from the left soleus, medial gastrocnemius and tibialis anterior. Whole-body balance, as measured by the anteroposterior forces and muscle responses, was quantified using frequency (coherence and gain functions) and time (cumulant density function) domain correlations with the vestibular stimuli. Old men exhibited a compressed frequency response of the vestibular reflex with a greater relative gain at lower frequencies for the plantar flexors and anteroposterior forces than young. In the time domain, the peak amplitude of the short latency response was 45-64% lower for the plantar flexors and anteroposterior forces (p≤0.05) in the old than young, but not for the tibialis anterior (p=0.21). The old men had a 190% and 31% larger medium latency response for only the tibialis anterior and anteroposterior forces, respectively, than young (p≤0.01). A strong correlation between the tibialis anterior and the force response was also detected (r=0.80, p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.01). In conclusion, net vestibular-evoked muscle responses led to smaller short and larger medium latency peak amplitudes in anteroposterior forces for the old. The present results likely resulted from a compressed and lower operational frequency range of the vestibular reflexes and the activation of additional muscles (tibialis anterior) to maintain standing balance.

Research paper thumbnail of Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

Clinical neurophysiology: official journal of the International Federation of Clinical Neurophysiology

To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular ... more To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P<0.05). NF jiggle was significantly higher in the TA compared to VM (P<0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P<0.05). For VM, NF jiggle was positively correlated ...

Research paper thumbnail of Increased neuromuscular transmission instability and motor unit remodelling with diabetic neuropathy as assessed using novel near fibre motor unit potential parameters

Clinical Neurophysiology, 2014

To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in... more To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in patients with diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG) and near fibre (NF) motor unit potential (MUP) parameters. The tibialis anterior (TA) muscle was tested in 12 patients with DPN (65 ± 15 years) and 12 controls (63 ± 15 years). DQEMG was used to analyze electromyographic (EMG) signals collected during voluntary contractions. MUP and NF MUP parameters were analyzed. NF MUPs were obtained by high-pass filtering MUP template waveforms, which isolates contributions of fibres that are close to the needle detection surface. NF MUP parameters provided assessment of motor unit size (NF area), fibre density (NF fibre count) and contribution dispersion (NF dispersion) and neuromuscular transmission instability (NF jiggle). DPN patients had larger (+45% NF area), more complex (+30% NF fibre count), and less stable (+30% NF jiggle) NF MUPs (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). No significant relationships were found between NF MUP stability and denervation, or strength; however NF MUP complexity was positively related to TA denervation in the DPN group (r=0.63; p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). NF MUP complexity and instability were positively related in DPN patients (r=0.46; p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). DPN is associated with neuromuscular transmission instability and MU remodelling that can be assessed using DQEMG. DQEMG-derived NF MUP parameters may be useful in identifying patients in early stages of neuromuscular dysfunction related to DPN.

Research paper thumbnail of Velocity dependence of eccentric strength in young and old men: the need for speed!

Applied physiology, nutrition, and metabolism = Physiologie appliquee, nutrition et metabolisme, Jan 3, 2015

Older adults better maintain eccentric strength relative to isometric strength, as indicated by a... more Older adults better maintain eccentric strength relative to isometric strength, as indicated by a higher ratio of eccentric:isometric torque as compared with younger adults. The effect of increasing angular velocities (>200°/s) on the age-related maintenance of eccentric strength has not been tested and thus it is unknown whether the eccentric:isometric ratio is velocity dependent in old age. The purpose of this study was to investigate eccentric strength of the ankle dorsiflexors over a large range of lengthening angular velocities in young and older men. Isometric neuromuscular properties were assessed on a HUMAC NORM dynamometer. Nine young (∼24 years) and 9 older (∼76 years) healthy men performed maximal voluntary eccentric contractions at angular velocities of 15-360°/s. Despite near full voluntary activation (>95%), the older men were ∼30% weaker than the young men for isometric strength (P < 0.05). Across all lengthening velocities, older men had a greater eccentric:...

Research paper thumbnail of Decreased muscle endurance associated with diabetic neuropathy may be attributed partially to neuromuscular transmission failure

Journal of Applied Physiology, 2015

Diabetic polyneuropathy (DPN) can cause muscle atrophy, weakness, contractile slowing and neuromu... more Diabetic polyneuropathy (DPN) can cause muscle atrophy, weakness, contractile slowing and neuromuscular transmission instability. Our objective was to assess the response of the impaired neuromuscular system of DPN in humans when stressed with a sustained maximal voluntary contraction (MVC). Baseline MVC and evoked dorsiflexor contractile properties were assessed in DPN patients (n=10) and controls (n=10). Surface electromyography (EMG) was used to record tibialis anterior evoked maximal compound muscle action potentials (CMAPs) and neuromuscular activity during MVCs. Participants performed a sustained isometric dorsiflexion MVC for which task termination was determined by the inability to sustain &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;60% MVC torque. The fatigue protocol was immediately followed by a maximal twitch, with additional maximal twitches and MVCs assessed at 30 seconds and 2 minutes post-fatigue. DPN patients fatigued ~21% more quickly than controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05) and featured less relative EMG activity during the first third of the fatigue protocol compared to controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). Immediately following fatigue, maximal twitch torque was reduced similarly (~20%) in both groups and concurrently CMAPs were reduced (~12%) in DPN patients, whereas they were unaffected in controls (p&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;0.05). Twitch torque and CMAP amplitude recovered to baseline 30-seconds post-fatigue. Additionally, at 30-seconds post-fatigue, both groups had similar (~10%) reductions in MVC torque relative to baseline, and MVC strength recovered by 2-minutes post-fatigue. We conclude DPN patients possess less endurance than controls, and neuromuscular transmission failure may contribute to this greater fatigability.

Research paper thumbnail of Increased motor unit potential shape variability across consecutive motor unit discharges in the tibialis anterior and vastus medialis muscles of healthy older subjects

Clinical Neurophysiology, 2015

To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular ... more To study the potential utility of using near fiber (NF) jiggle as an assessment of neuromuscular transmission stability in healthy older subjects using decomposition-based quantitative electromyography (DQEMG). The tibialis anterior (TA) and vastus medialis (VM) muscles were tested in 9 older men (77±5years) and 9 young male control subjects (23±0.3years). Simultaneous surface and needle-detected electromyographic (EMG) signals were collected during voluntary contractions, and then analyzed using DQEMG. Motor unit potential (MUP) and NF MUP parameters were analyzed. NF jiggle was significantly increased for both the TA and VM in the old age group relative to the younger controls (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). NF jiggle was significantly higher in the TA compared to VM (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). For TA, NF jiggle was negatively correlated with MUNE, and positively correlated with S-MUP amplitude, NF count, MUP duration, MUP peak-to-peak voltage, and MUP area (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05). For VM, NF jiggle was positively correlated with NF count and MUP area (P&amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt;0.05), and no significant correlations were found between NF jiggle and S-MUP amplitude, MUP duration, or MUP peak-to-peak voltage (MUNE was not calculated for VM, so no correlation could be made). Healthy aging is associated with neuromuscular transmission instability (increased NF jiggle) and MU remodeling, which can be measured using DQEMG. NF jiggle derived from DQEMG can be a useful method of identifying impairment with neuromuscular dysfunction at various stages of MU remodeling and aging.

Research paper thumbnail of Increased neuromuscular transmission instability and motor unit remodelling with diabetic neuropathy as assessed using novel near fibre motor unit potential parameters

Clinical Neurophysiology

Objective To assess the degree of neuromuscular transmission variability and motor unit (MU) remo... more Objective To assess the degree of neuromuscular transmission variability and motor unit (MU) remodelling in patients with diabetic polyneuropathy (DPN) using decomposition-based quantitative electromyography (DQEMG) and near fibre (NF) motor unit potential (MUP) parameters. Methods The tibialis anterior (TA) muscle was tested in 12 patients with DPN (65±15 yrs) and 12 controls (63±15 yrs). DQEMG was used to analyze electromyographic (EMG) signals collected during voluntary contractions. MUP and NF MUP parameters were analyzed. NF MUPs were obtained by high-pass filtering MUP template waveforms, which isolates contributions of fibres that are close to the needle detection surface. NF MUP parameters provided assessment of motor unit size (NF area), fibre density (NF fibre count) and contribution dispersion (NF dispersion) and neuromuscular transmission instability (NF jiggle). Results DPN patients had larger (+45% NF area), more complex (+30% NF fibre count), and less stable (+30% NF ...

Research paper thumbnail of Shortening-induced torque depression in old men: implications for age-related power loss

Experimental gerontology, 2014

Following active muscle shortening, the steady-state isometric torque at the final muscle length ... more Following active muscle shortening, the steady-state isometric torque at the final muscle length is lower than the steady-state torque obtained for a purely isometric contraction at that same final muscle length. This well-documented property of skeletal muscle is termed shortening-induced torque depression (TD). Despite many investigations into the mechanisms of weakness and power loss in old age, the influence of muscle shortening on the history dependence of isometric torque production remains to be elucidated. Thus, it is unclear whether older adults are disadvantaged for torque and power production following a dynamic shortening contraction. The purpose of this study was to evaluate shortening-induced TD in older adults, and to determine whether shortening-induced TD is related to power loss. Maximal voluntary isometric dorsiflexion contractions (MVC; 10s) in 8 young (25.5±3.7years) and 9 old (76.1±5.4years) men were performed on a HUMAC NORM dynamometer as a reference, and the...

Research paper thumbnail of Decay of force transients following active stretch is slower in older than young men: support for a structural mechanism contributing to residual force enhancement in old age

Journal of biomechanics, Jan 17, 2014

Following active lengthening of muscle, force reaches an isometric steady state above that which ... more Following active lengthening of muscle, force reaches an isometric steady state above that which would be achieved for a purely isometric contraction at the same muscle length. This fundamental property of muscle, termed "residual force enhancement (RFE)," cannot be predicted by the force-length relationship, and is unexplained by the cross-bridge theory of muscle contraction. Recently, we showed that older adults experience higher RFE than young for the ankle dorsiflexors primarily owing to a greater reliance on passive force enhancement (PFE) and similar RFE for the knee extensors but a greater contribution of PFE to total RFE. Natural adult aging may prove a useful model in exploring mechanisms of RFE which may reside in the dissipation of force transients following stretch. A post-hoc analysis was conducted on previously described RFE experiments in young (~26 years) and old (~77 years) men for the dorsiflexors and knee extensors to fit the force following stretch with...

Research paper thumbnail of The relationship between blood pressure and sciatic nerve blood flow velocity in rats with insulin-treated experimental diabetes

Diabetes & vascular disease research : official journal of the International Society of Diabetes and Vascular Disease, Jan 22, 2014

Peripheral nerve blood flow (NBF) does not autoregulate but, instead, responds passively to chang... more Peripheral nerve blood flow (NBF) does not autoregulate but, instead, responds passively to changes in mean arterial pressure (MAP). How this relationship is impacted by insulin-treated experimental diabetes (ITED) is unknown. We tested the hypothesis that ITED will reduce NBF across a range of MAP in Sprague Dawley rats. Following 10 weeks of control or ITED conditions, conscious MAP (tail-cuff) was measured, and under anaesthesia, the MAP (carotid artery catheter, pressure transducer) and NBF (Doppler ultrasound, 40 MHz) responses to sodium nitroprusside (60 µg/kg) and phenylephrine (12 µg/kg) infusion were recorded (regression equations for MAP vs NBF were created for each rodent). Thereafter, motor nerve conduction velocity (MNCV) and nerve vascularization (haematoxylin and eosin stain) were determined. Conscious MAP was higher and MNCV was lower in the ITED group (p < 0.01). In response to drug infusions, the ΔMAP and ΔNBF were similar between groups (p ≥ 0.18). Estimated co...

Research paper thumbnail of The effect of knee joint angle on plantar flexor power in young and old men

Experimental Gerontology, 2014

Human adult aging is associated with a loss of strength, contractile velocity and hence, power. T... more Human adult aging is associated with a loss of strength, contractile velocity and hence, power. The principal plantar flexors, consisting of the bi-articular gastrocnemeii and the mono-articular soleus, appear to be affected differently by the aging process. However, the age-related effect of knee joint angle on the torque-angular velocity relationship and power production of this functionally important muscle group is unknown. The purpose was to determine whether flexing the knee, thereby reducing the gastrocnemius contribution to plantar flexion, would exacerbate the age-related decrements in plantar flexion power, or shift the torque-angular velocity relationship differently in older compared with young men. Neuromuscular properties were recorded from 10 young (~25 y) and 10 old (~78 y) men with the knee extended (170°) and flexed (90°), in a randomized order. Participants performed maximal voluntary isometric contractions (MVCs), followed by maximal velocity-dependent shortening contractions at pre-set loads, ranging from 15 to 75% MVC. The young men were~20-25% stronger, 12% faster and~30% more powerful than the old for both knee angles (P b 0.05). In both age groups, isometric MVC torque was~17% greater in the extended than flexed knee position, with no differences in voluntary activation (N95%). The young men produced 7-12% faster angular velocities in the extended knee position for loads ≤30% MVC, but no differences at higher loads; whereas there were no detectable differences in angular velocity between knee positions in the old across all relative loads. For both knee angles, young men produced peak power at 43.3 ± 9.0% MVC, whereas the old men produced peak power at 54.8 ± 7.9% MVC. These data indicate that the young, who have faster contracting muscles compared with the old, can rely more on velocity than torque for generating maximal power.

Research paper thumbnail of Torque loss induced by repetitive maximal eccentric contractions is marginally influenced by work-to-rest ratio

European Journal of Applied Physiology, 2004

The influence of different work-to-rest (W:R) ratios during fatigue induced by maximal eccentric ... more The influence of different work-to-rest (W:R) ratios during fatigue induced by maximal eccentric contractions is unknown. The present study sought to expand the understanding of the task-dependent nature of eccentric contractions, and the associated fatigue, during exercise and acute as well as extended recovery periods. Using a Biodex multi-joint dynamometer, the ankle dorsiflexors of eight men [26 (4) years] were fatigued with 150 maximal eccentric contractions. Set structure was manipulated such that one leg performed 3 sets of 50 repetitions (short rest protocol, SRP), and the other leg performed 15 sets of 10 repetitions (long rest protocol, LRP). A 1-min rest interval separated each set, which resulted in 2 and 14 min of total rest for the SRP and the LRP, respectively. At fatigue, the SRP demonstrated a marginally greater loss of average peak eccentric torque than the LRP (P<0.05). In the acute period following fatigue, isometric peak torque loss and the degree of lowfrequency fatigue (LFF) were not recovered (P<0.05) and were equivalent for both protocols. Significant impairment of both eccentric and isometric torque was persistent and equal for each protocol at 96 h of recovery (P<0.05). These findings suggest that the W:R ratio has a modest influence on the fatigue (torque loss) induced by maximal eccentric contractions, but maximal isometric torque during recovery and LFF are insensitive to changes in total rest time.

Research paper thumbnail of Length dependent loss of motor axons and altered motor unit properties in human diabetic polyneuropathy

Clinical Neurophysiology, 2014

Patients with diabetic polyneuropathy (DPN) have fewer motor units in a lower (tibialis anterior ... more Patients with diabetic polyneuropathy (DPN) have fewer motor units in a lower (tibialis anterior [TA]) and upper limb (first dorsal interosseous [FDI]) muscle compared to age-matched controls. Neuromuscular properties of TA are more severely affected in DPN than FDI as demonstrated by the degree of motor unit loss, and increased MUP complexity. DQEMG-derived MUNE may provide a more sensitive or useful complementary measure of early involvement of the motor system in DPN versus results of standard motor nerve conduction studies.

Research paper thumbnail of Exercise Training Enhances Insulin-Stimulated Nerve Arterial Vasodilation in Rats with Insulin-Treated Experimental Diabetes

AJP: Regulatory, Integrative and Comparative Physiology, 2014

Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechani... more Insulin stimulates nerve arterial vasodilation through a nitric oxide (NO) synthase (NOS) mechanism. Experimental diabetes reduces vasa nervorum NO reactivity. Studies investigating hyperglycemia and nerve arterial vasodilation typically omit insulin treatment and use sedentary rats resulting in severe hyperglycemia. We tested the hypotheses that 1) insulin-treated experimental diabetes and inactivity (DS rats) will attenuate insulin-mediated nerve arterial vasodilation, and 2) deficits in vasodilation in DS rats will be overcome by concurrent exercise training (DX rats; 75-85% VO2 max, 1 h/day, 5 days/wk, for 10 wk). The baseline index of vascular conductance values (VCi = nerve blood flow velocity/mean arterial blood pressure) were similar (P ≥ 0.68), but peak VCi and the area under the curve (AUCi) for the VCi during a euglycemic hyperinsulinemic clamp (EHC; 10 mU·kg(-1)·min(-1)) were lower in DS rats versus control sedentary (CS) rats and DX rats (P ≤ 0.01). Motor nerve conduction velocity (MNCV) was lower in DS rats versus CS rats and DX rats (P ≤ 0.01). When compared with DS rats, DX rats expressed greater nerve endothelial NOS (eNOS) protein content (P = 0.04). In a separate analysis, we examined the impact of diabetes in exercise-trained rats alone. When compared with exercise-trained control rats (CX), DX rats had a lower AUCi during the EHC, lower MNCV values, and lower sciatic nerve eNOS protein content (P ≤ 0.03). Therefore, vasa nervorum and motor nerve function are impaired in DS rats. Such deficits in rats with diabetes can be overcome by concurrent exercise training. However, in exercise-trained rats (CX and DX groups), moderate hyperglycemia lowers vasa nervorum and nerve function.

Research paper thumbnail of Motor Unit Survival in Lifelong Runners Is Muscle Dependent

Medicine & Science in Sports & Exercise, 2012

A contributing factor to the loss of muscle mass and strength with adultaging is the reduction in... more A contributing factor to the loss of muscle mass and strength with adultaging is the reduction in the number of functioning motor units (MUs). Recently, we reportedthat life-long competitive runners (masters runners; ~66y) had greater numbers of MUs in a leg muscle (tibialis anterior) than age-matched recreationally active controls. This suggested that chronic exposure to high levels of physical activity may limit the loss of MU numbers with adultaging. However, it is unknown if this finding is the result of chronic activation of the specificallyexercised motoneuron (MN) pool (i.e., tibialis anterior), or an overall systemic neuroprotective effect of high levels of physical activity. Purpose: The purposewas to estimate the number of functioning MUs (MUNEs) in the bicepsbrachii (an upper body muscle not directly loaded by running) of 9 young (27±5y) and 9 old (70±5y) men, and 9 life-long competitive masters runners (67±4y).