Isometric abduction muscle activation in patients with rotator tendinosis of the shoulder (original) (raw)
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European Journal of Applied Physiology, 2008
Altered shoulder muscle activity is frequently believed to be a pathogenetic factor of subacromial impingement (SI) and therapeutic interventions have been directed towards restoring normal motor patterns. Still, there is a lack of scientific evidence regarding the changes in muscle activity in patients with SI. The aim of the study was to determine and compare the activity pattern of the shoulder muscles in subjects with and without SI. Twenty-one subjects with SI and 20 healthy controls were included. Electromyography (EMG) was assessed from eight shoulder muscles from both shoulders during motion. In the symptomatic shoulder, there was a significantly greater EMG activity during abduction in the supraspinatus and latissimus muscles and less activity in serratus anterior compared to the healthy subjects. During external rotation, there was significantly less activity of the infraspinatus and serratus anterior muscles on the symptomatic side compared to the healthy subjects. On the asymptomatic side, the groups showed different muscle activity during external rotation. Our findings of an altered shoulder muscle activity pattern on both the symptomatic and asymptomatic side in patients indicate that the different motor patterns might be a pathogenetic factor of SI, perhaps due to inappropriate neuromuscular strategies affecting both shoulders.
Journal of Electromyography and Kinesiology, 2000
Studies have shown an increased muscle activation at the opposite passive side during unilateral contractions. The purpose of the present study was to examine the influence of pain on muscle activation in the passive shoulder during unilateral shoulder abduction. Ten patients with unilateral rotator tendinosis of the shoulder and nine healthy controls performed unilateral maximal voluntary contractions (MVC) and sustained submaximal contractions with and without subacromial injections of local anaesthetics of the afflicted shoulder. Muscle activation was recorded by electromyography (EMG) from the trapezius, deltoid, infraspinatus and supraspinatus muscles in both shoulders. During MVCs, the EMG amplitude from muscles of the passive afflicted side was not different in patients and controls, and was not influenced by pain alterations. In contrast, the EMG amplitude from the muscles of the passive unafflicted side was lower in the patients and increased after pain reduction. During the sustained submaximal contraction the EMG amplitude increased gradually in the passive shoulder to 15-30% of the EMG amplitude observed during MVC. This response was not influenced by differences in pain. We conclude that muscle activation of the passive shoulder was closely related to the activation of the contracting muscles and thus related to central motor drive, and not directly influenced by changes in pain.
The influence of experimental muscle pain on motor unit activity during low-level contraction
European Journal of Applied Physiology, 2000
In the present study we compared motor unit (MU) activity in a painful extensor carpi ulnaris (ECU) muscle to that of a pain-free control. According to the pain adaptation model the activity of the painful ECU muscle may be inhibited and its antagonist activity increased during wrist extension performed as a pre-de®ned low-force ramp. The pre-de®ned low force may then be maintained by increased activity in the pain-free synergist muscles such as the extensor carpi radialis (ECR) muscle. Nine females (31±47 years old) participated in the study. Maximal voluntary contraction (MVC) of the wrist extensors was performed. A catheter was inserted into the ECU muscle to allow the injection of hypertonic saline to evoke muscle pain, and a concentric needle was inserted for the recording of MU activity. Surface electromyograms were recorded from a synergist and an antagonist (ECR and¯exor carpi radialis) to the painful ECU muscle. A force ramp of isometric wrist extensions up to 10% MVC, with a force increase of 1% MVC á s )1 , were performed followed by 60 s of sustained contraction at 10% MVC. The number of MUs recruited was almost identical for baseline and with pain, and no eect of experimental muscle pain was found on the properties of the MUs (amplitude, area) or their ®ring characteristics (mean ®ring rate, ®ring variability) during low-force ramp contraction. During the sustained 10% MVC, no eect of pain was found for concentric or surface EMG of the forearm muscles. At low force levels no pain-induced modulations were found in MU activity, when the mechanical condition was similar to that of a control situation.
Clinical Neurophysiology, 2004
Objective: In the present study, the influence of experimental muscle pain on muscle coordination and fatigue development during sustained isometric elbow flexion was investigated. Methods: Conventional surface electromyography (EMG) was recorded from the biceps brachii, brachioradialis, deltoideus and trapezius muscle during isometric elbow flexion at 40% maximum force. Single motor unit (MU) conduction velocity in the biceps brachii was assessed using a high spatial resolution surface EMG technique. Measurements were performed on 15 healthy subjects before, during and after (1) injection of hypertonic (pain condition) and (2) isotonic saline (control) into the biceps brachii. The pain intensity was assessed on a 10 cm visual analogue scale. Results: The experimental results showed in both experimental sessions a fatigue-related increase of the root mean square value of EMG (222^164% of the baseline), and a decrease of the median frequency (118^16% of the baseline) in all investigated muscles. A maximum pain level of in average 3.2 cm on the visual analogue scale was reached after injection of hypertonic saline during contraction. Differences between painful and control condition were seen in an increased trapezius activity (230^141%) during pain. The global EMG activity of the brachioradialis and biceps brachii was unaffected by experimental muscle pain in line with unaffected single MU conduction velocity in the biceps brachii. Differences in endurance time (mean 89.3 and 102.3 s, pain and control, respectively) were not significant. Conclusions/Significance: The findings suggest that upper extremity pain could be a possible source for overloading the trapezius muscle and as such is an important factor in occupational settings.
Journal of Applied Physiology, 2004
Søgaard. Intramuscular pressure and EMG relate during static contractions but dissociate with movement and fatigue. pressure (IMP) and electromyography (EMG) mirror muscle force in the nonfatigued muscle during static contractions. The present study explores whether the constant IMP-EMG relationship with increased force may be extended to dynamic contractions and to fatigued muscle. IMP and EMG were recorded from shoulder muscles in three sessions: 1) brief static arm abductions at angles from 0 to 90°, with and without 1 kg in the hands; 2) dynamic arm abductions at angular velocities from 9 to 90°/s, with and without 1 kg in the hands; and 3) prolonged static arm abduction at 30°for 30 min followed by recovery. IMP and EMG increased in parallel with increasing shoulder torque during brief static tasks. During dynamic contractions, peak IMP and EMG increased to values higher than those during static contractions, and EMG, but not IMP, increased significantly with speed of abduction. In the nonfatigued supraspinatus muscle, a linear relationship was found between IMP and EMG; in contrast, during fatigue and recovery, significant timewise changes of the IMP-to-EMG ratio occurred. The results indicate that IMP should be included along with EMG when mechanical load sharing between muscles is evaluated during dynamic and fatiguing contractions.
Isometric contractions induced by neuromuscular electrostimulation (NMES) have been shown to result in a prolonged force decrease but the time course of the potential central and peripheral factors have never been investigated. This study examined the specific time course of central and peripheral factors after isometric NMES-induced muscle damage. Twentyfive young healthy men were subjected to an NMES exercise consisting of 40 contractions for both legs. Changes in maximal voluntary contraction force of the knee extensors (MVC), peak evoked force during double stimulations at 10 Hz (Db 10 ) and 100 Hz (Db 100 ), its ratio (10:100), voluntary activation, muscle soreness and plasma creatine kinase activity were assessed before, immediately after and throughout four days after NMES session. Changes in knee extensors volume and T 2 relaxation time were also assessed at two (D2) and four (D4) days post-exercise. MVC decreased by 29% immediately after NMES session and was still 19% lower than the baseline value at D4. The decrease in Db 10 was higher than in Db 100 immediately and one day post-exercise resulting in a decrease (212%) in the 10:100 ratio. On the contrary, voluntary activation significantly decreased at D2 (25%) and was still depressed at D4 (25%). Muscle soreness and plasma creatine kinase activity increased after NMES and peaked at D2 and D4, respectively. T 2 was also increased at D2 (6%) and D4 (9%). Additionally, changes in MVC and peripheral factors (e.g., Db 100 ) were correlated on the full recovery period, while a significant correlation was found between changes in MVC and VA only from D2 to D4. The decrease in MVC recorded immediately after the NMES session was mainly due to peripheral changes while both central and peripheral contributions were involved in the prolonged force reduction. Interestingly, the chronological events differ from what has been reported so far for voluntary exercise-induced muscle damage.
Short-Term Immobilization after Eccentric Exercise. Part I: Contractile Properties
Medicine & Science in Sports & Exercise, 2003
Purpose: The purpose of this study was to examine the compound muscle action potential (M-wave) and evoked contractile properties of immobilized muscle after high-force eccentric exercise. We believed that changes in these variables would contribute to the enhanced recovery of maximal voluntary force observed after short-term immobilization of damaged muscle. We hypothesized that immobilization after eccentric exercise would result in an enhanced M-wave and a change in contractile properties toward characteristics of faster muscle fibers. Methods: Twenty-five college-age males were matched according to force loss after 50 maximal eccentric contractions of the elbow flexors and placed into an immobilization (IMM, N ϭ 12) or control (CON, N ϭ 13) group. IMM had their arm immobilized at 90°and secured in a sling during a 4-d treatment. Maximal isometric torque (MVC) was assessed at baseline and for 8 d after treatment. M-wave and evoked contractile properties of the muscle (twitch torque [TT], maximal rate of torque development [MRTD], time to peak torque [TPT], and one-half relaxation time [HRT]) were assessed at baseline and for the first 5 d after treatment. Results: Immediately postexercise, MVC was reduced 43% and 42% in IMM and CON, respectively. Recovery of MVC was significantly greater in IMM during recovery (P Ͻ 0.05), 95% of baseline MVC compared with 83% in CON. M-wave was reduced 32%, and all contractile properties were altered immediately postexercise. M-wave, MRTD, TPT, and HRT were not significantly different between groups during recovery (P Ͼ 0.05). TT demonstrated enhanced recovery in IMM (P Ͻ 0.05). Conclusions: Short-term immobilization after eccentric exercise resulted in enhanced recovery of maximal voluntary force. However, enhanced force recovery cannot be explained by muscle activation and evoked contractile properties of the muscle.
Journal of Electromyography and Kinesiology, 2007
The purpose of this study was to investigate the influence of eccentric contractions (ECC) on the biceps (BB) and triceps brachii (TB) muscles during maximal voluntary contraction (MVC) of elbow flexors using electrical (EMG) and mechanomyographical activities (MMG). Each of 18 male students performed 25 submaximal contractions (50% MVC) of the elbow flexors. Root mean square amplitude (RMS) and median frequency (MDF) were calculated for the EMG and MMG signals recorded during MVC. All measurements were taken before, immediately after, 24, 48, 72, and 120 h post-ECC from the BB and TB muscles. MVC was reduced by 34% immediately after exercise and did not return to the resting value within 120 h (P 6 0.05). The EMG MDF decreased significantly (P 6 0.05) in both muscles after ECC. The MMG RMS at 24 h, 48, 72 and 120 h post-ECC was significantly lower compared to that recorded immediately after ECC in both muscles (P 6 0.05). The present research showed that (i) there were similar changes in electrical and mechanical activities during MVC after submaximal ECC in agonist and antagonist muscles suggesting a common drive controlling the agonist and antagonist motoneuron pool, (ii) the ECC induced different changes in EMG than in MMG immediately after ECC and during 120 h of recovery that suggested an increased tremor and contractile impairments, i.e., reduced rate of calcium release from the sarcoplasmic reticulum (acute effect), and changes in motor control mechanisms of agonist and antagonist muscles, and increased muscle stiffness (chronic effect).