James Bagley | San Francisco State University (original) (raw)

Papers by James Bagley

Strength and Conditioning Journal, May 1, 2015

The biochemist, Dec 22, 2022

Busting muscle myths Skeletal muscle is the most abundant tissue in the human body. Known for its... more Busting muscle myths Skeletal muscle is the most abundant tissue in the human body. Known for its primary role in movement, muscle also plays important roles in regulating metabolism, maintaining body temperature and providing large stores of protein, carbohydrates and fats. Muscle cells (known as 'muscle fibres') can rapidly adapt to exercise or disuse by changing size and function. Many myths and misconceptions have proliferated through the years related to skeletal muscle, exercise training and human performance. Some of these myths have spanned centuries, but more recent research has passed doubt on these stories. In this article, we address common misconceptions, including the 'go big or go home' and 'if you don't use it, you lose it' approaches to training. Clarification of these myths could positively impact individual exercise programs/therapies and their outcomes.

Access to thesis permanently restricted to Ball State community only.Access to abstract permanent... more Access to thesis permanently restricted to Ball State community only.Access to abstract permanently restricted to Ball State community only.School of Physical Education, Sport, and Exercise ScienceThesis (Ph. D.

Physiological Reports, Dec 1, 2019

In 2007 the National Institutes of Health launched the Human Microbiome Project (HMP), an interdi... more In 2007 the National Institutes of Health launched the Human Microbiome Project (HMP), an interdisciplinary research initiative seeking to characterize the contribution of human gut microbiota to health and disease (Turnbaugh et al., 2007). Subsequent findings have demonstrated compelling relationships between human gut microbiome composition and many leading causes of death worldwide including cardiovascular disease (Wang et al., 2011), diabetes (Larsen et al., 2010), and cancer (Ahn et al., 2013). Although the gut microbiome is suggested to exhibit exceptional plasticity (Gomez et al., 2019), a detailed understanding of the factors determining human microbiome assembly is lacking (Relman, 2015).

The Journal of Physiology, Jan 30, 2023

Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. ... more Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined ‘domains’ to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA‐sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease. image

Medicine and Science in Sports and Exercise, May 1, 2018

Medicine and Science in Sports and Exercise, May 1, 2017

METHODS: 23 early pubertal children (16 F; 7-11 years) and 15 young adults (7 F; 21-35 years) und... more METHODS: 23 early pubertal children (16 F; 7-11 years) and 15 young adults (7 F; 21-35 years) underwent an incremental ramp exercise test on a cycle ergometer. Pulmonary gas exchange was measured breath-by-breath (Vmax, Carefusion). Vastus lateralis [HHb] was quantified by TRS-NIRS (TRS-21, Hamamatsu Photonics). RESULTS: Peak VO 2 was not different between children and adults normalized to body mass (46.7±8.1 vs. 48.9±7.7 mL/min/kg). Absolute [HHb] was not different between children and adults during unloaded pedaling (23.5±5.5 vs 26.8±10.0 uM, p=0.20) but adults had a higher peak exercise [HHb] (32.0±8.2 vs 44.4±22.6 uM, p=0.01). Two way RM-ANOVA of relative HHb dynamics revealed an effect of age (F(1,36) = 6.895, p=0.013) and interaction with % peak power (p=0.001, Figure). Post-hoc, relative HHb was lower at 60% peak power in children vs adults (57±10% vs 68±13%, p=0.0006), while VO 2 did not differ (33.5±4.9% vs 30.6±6.2%, p=0.12). CONCLUSION: Muscle deoxygenation is both attenuated and delayed during incremental exercise in children compared to adults, despite similar relative VO 2. This is consistent with a closer matching of muscle microvascular O 2 delivery to utilization over a greater range of aerobic power in children. The mechanisms contributing to this improved regulation of muscle blood flow during exercise in children warrant further study.

Background: Metabolic carts measure the carbon dioxide (CO 2) produced and oxygen consumed by an ... more Background: Metabolic carts measure the carbon dioxide (CO 2) produced and oxygen consumed by an individual when breathing to assess metabolic fuel usage (carbohydrates versus fats). However, these systems are expensive, time-consuming, and only available in health care laboratory settings. A small handheld device capable of determining metabolic fuel usage via CO 2 from exhaled air has been developed. Objective: The aim of this study is to evaluate the validity of a novel handheld device (Lumen) for measuring metabolic fuel utilization in healthy young adults. Methods: Metabolic fuel usage was assessed in healthy participants (n=33; mean age 23.1 years, SD 3.9 years) via respiratory exchange ratio (RER) values obtained from a metabolic cart as well as % CO 2 from the Lumen device. Measurements were performed at rest in two conditions: fasting, and after consuming 150 grams of glucose, in order to determine changes in metabolic fuel usage. Reduced major axis regression and simple linear regression were performed to test for agreement between RER and Lumen % CO 2. Results: Both RER and Lumen % CO 2 significantly increased after glucose intake (P<.001 for both) compared with fasting conditions, by 0.089 and 0.28, respectively. Regression analyses revealed an agreement between the two measurements (F 1,63 =18.54; P<.001). Conclusions: This study shows the validity of Lumen for detecting changes in metabolic fuel utilization in a comparable manner with a laboratory standard metabolic cart, providing the ability for real-time metabolic information for users under any circumstances.

Frontiers in rehabilitation sciences, Aug 8, 2022

Background: Virtual exercise has become more common as emerging and converging technologies make ... more Background: Virtual exercise has become more common as emerging and converging technologies make active virtual reality games (AVRGs) a viable mode of exercise for health and fitness. Our lab has previously shown that AVRGs can elicit moderate to vigorous exercise intensities that meet recommended health benefit guidelines. Dissociative attentional focuses during AVRG gameplay have the potential to widen the gap between participants' perception of exertion and actual exertion. Objective: The aim of this study was to determine actual exertion (AEx) vs. perceived exertion (PEx) levels during AVRGs by measuring heart rate (HR) and ratings of perceived exertion (RPE) in two di erent settings. Materials and methods: HR and RPE were collected on participants (N = ; age. ± .) during min of gameplay in LabS and GymS using the HTC VIVE with the following games played: Fruit Ninja VR (FNVR), Beat Saber (BS), and Holopoint (HP). Results: Participants exhibited significantly higher levels of AEx compared to reported PEx for all three AVRGs (Intensity): FNVR [AEx =. ±. (Light), PEx =. ±. (Very Light)], BS [AEx =. ±. (Light), PEx =. ±. (Very Light)], HP [AEx =. ±. (Somewhat Hard), PEx =. ±. (Light-Somewhat Hard)]. Additionally, participants playing in the GymS experienced significantly higher levels of AEx [. ±. (Light-Somewhat Hard)] and PEx [. ±. (Very Light-Light)] compared to the LabS [AEx =. ±. (Light), PEx =. ±. (Very Light-Light)]. Conclusion: Perceptions of exertion may be lower than actual exertion during AVRG gameplay, and exertion levels can be influenced by the setting in which AVRGs are played. This may inform VR developers and health clinicians who aim to incorporate exercise/fitness regimens into upcoming 'virtual worlds' currently being developed at large scales (i.e., the "metaverse").

Strength and Conditioning Journal, Dec 1, 2016

Medicine & Science in Sports & Exercise, 2020

210 Board #26 May 27 9:30 AM 11:00 AM Effect Of Exercise Setting On Energy Expenditure And Enjoym... more 210 Board #26 May 27 9:30 AM 11:00 AM Effect Of Exercise Setting On Energy Expenditure And Enjoyment During Active Virtual Reality Gaming Trenton Huynh Stewart, Kirsten Villanueva, Amanda Hahn, Julissa Ortiz, Chandler Wolf, Randy Nguyen, Nicole D. Bolter, Marialice Kern, FACSM, James R. Bagley. San Francisco State University, San Francisco, CA. (Sponsor: Marilice Kern, FACSM) Email: tstewar1@sfsu.edu

Medicine & Science in Sports & Exercise, 2020

BackgroundMetabolic carts measure the carbon dioxide produced and oxygen consumed from the breath... more BackgroundMetabolic carts measure the carbon dioxide produced and oxygen consumed from the breath in order to assess metabolic fuel usage (carbohydrates vs. fats). However, these systems are expensive, time-consuming, and only available in the clinic. A small hand-held device capable of measuring metabolic fuel via CO2from exhaled air has been developedObjectiveTo evaluate the validity of a novel hand-held device (Lumen®) for measuring metabolic fuel utilization in healthy young adultsMethodsMetabolic fuel usage was assessed in healthy participants (n = 33; age: 23.1 ± 3.9 y) via respiratory exchange ratio (RER) values from the “gold-standard” metabolic cart as well as %CO2from the Lumen device. Measurements were performed at rest in two conditions, fasting, and after consuming 150 grams of glucose in order to determine changes in metabolic fuel. Reduced major axis regression was performed as well as Bland-Altman plots and linear regressions to test for agreement between RER and Lum...

Medicine & Science in Sports & Exercise, 2017

Medicine & Science in Sports & Exercise, 2017

PURPOSE: Bioelectrical impedance analysis (BIA) scales have gained popularly in monitoring fitnes... more PURPOSE: Bioelectrical impedance analysis (BIA) scales have gained popularly in monitoring fitness progress at home, yet their accuracy is unknown. We assessed the validity and reliability of body fat percentage (BF%) measurements from a consumer bioelectrical analysis (cBIA) scale compared to the “gold standard” of hydrostatic weighing (HW). METHODS: Forty-three [male (n=22); female (n=21)] healthy volunteers [age: 27.9±5.6y; height: 170.0±8.6cm; mass: 69.0±13.7kg; body mass index (BMI) range: 16.8-33.1] arrived at the laboratory 3h fasted after 12h without exercise and underwent measures of residual lung volume (for HW calculations), hydration status, and BF% via cBIA scale (‘Lean’ and ‘Regular’ modes) and HW. We assessed cBIA scale validity using Bland-Altman Plots (identifying Mean Biases±Limits of Agreement) and reliability using intraclass correlation coefficients (ICC). RESULTS: With HW as the validity criterion, mean BF% was 22.3±6.1% for all participants (range: 5.3-35.8%; male mean: 20.8±6.4%; female mean: 23.9±5.5%). Compared to HW, the cBIA scale in ‘Lean’ mode underestimated BF% by -5.3±9.1% for all participants (males: -7.9±6.9%; females: -2.6±8.0%) (p≤0.05). In ‘Regular’ mode, the cBIA scale agreed with HW for all participants (BF% -0.8±9.3%; p=0.27) and females (BF% 0.4±10.8%; p=0.73); however, there was a significant difference for males (BF% 2.0±7.1%; p≤0.05). The cBIA was reliable when comparing day-to-day (‘Lean’ mode: 0.5±1.0%, ICC:0.99; ‘Regular’ mode: 0.4±1.0%, ICC:0.99) and week-to-week (‘Lean’ mode: -0.4±1.4%, ICC:0.98; ‘Regular’ mode: -0.2±1.5%, ICC:0.97) BF% for all participants. CONCLUSIONS: Compared to HW, the cBIA underestimated BF% in ‘Lean’ mode, and this discrepancy was more pronounced in males. However, the cBIA scale agreed with HW when analyzing BF% in ‘Regular’ mode for all participants and females, signifying the “mode” chosen on consumer BIA devices greatly impacts validity. The cBIA was reliable when comparing day-to-day and week-to-week BF% measures for all participants, suggesting this can be a reliable at-home BF% analysis scale.

Medicine & Science in Sports & Exercise, 2016

We caused myocardial infarction via ligation of the left anterior descending coronary artery to i... more We caused myocardial infarction via ligation of the left anterior descending coronary artery to induce CHF in mice, while sham animals received identical surgical procedures except ligation. We performed experiments 14-16 weeks post-surgery, and tested contractile properties of permeabilized diaphragm single fibers with or without exposure to the thiol-reducing agent dithiothreitol (DTT, 10 mM for 10min) prior to calcium activation. RESULTS: Maximal specific force (sFo) of diaphragm fibers was decreased in CHF compared to sham (in kN•m-2, 132.3 ±6.5 and 96.9 ±6.0), and sFo of fibers from CHF mice was increased by DTT treatment (126.3 ±6.6 kN•m-2). The rate constant of tension redevelopment (Ktr) was slower in CHF diaphragm fibers than sham (in s-1 44.12 ±3.9 and 31.26 ±2.4), and DTT treatment increased Ktr (41.4 ±1.7 s-1). Calcium sensitivity was unchanged by either CHF or DTT treatment. DTT had no effect on the single fiber contractile parameters (sFo, Ktr and pCa50) in sham animals. CONCLUSIONS: Our findings suggest that reversible thiol oxidation of sarcomeric proteins is a molecular mechanism of diaphragm fiber contractile dysfunction in CHF.

Isokinetics and Exercise Science, 2016

BACKGROUND: Anaerobic fatigue is a limiting factor in performance and athletes are often tested t... more BACKGROUND: Anaerobic fatigue is a limiting factor in performance and athletes are often tested to determine their fatigue resistance. Administering the classic Thorstensson test of fatigability is a popular method to determine fatigue percentage as it requires 50 maximal knee extension repetitions. However, there has been little research to determine whether performing more or fewer repetitions yields similar results. OBJECTIVE: The purpose of this study was to compare concentric fatigue percentage (FP) between the classic Thorstensson test (CT; average of first 3 repetitions to average of last 3 repetitions) and three different repetition ranges: peak torque repetition to repetition 30 (P30), peak torque repetition to repetition 50 (P50), and peak torque repetition to repetition 60 (P60). METHODS: Fifteen resistance trained men (age = 24.8 ± 1.3 yrs; height = 178.9 ± 5.1 cm; mass = 82.2 ± 8.0 kg) volunteered to perform 60 maximal concentric knee extension repetitions at 180 • /s on an isokinetic dynamometer, measuring peak torque of each repetition. RESULTS: P30 (r = 0.81) and P50 (r = 0.77) were highly correlated with CT but P60 (r = 0.58) was only moderately correlated with CT. P30 FP (44.7 ± 8.8) was significantly less than CT (62.3 ± 6.0), P50 (66.0 ± 6.8) and P60 (69.7 ± 7.1). CONCLUSION: FP can be determined through fewer repetitions of a knee extension fatigue test on an isokinetic dynamometer. While both P30 and P50 were highly correlated with CT, performing fewer repetitions requires less time to complete as well as less residual fatigue. When measuring knee extension FP, the number of repetitions performed in the test may be reduced to 30 while still maintaining a high correlation to a longer method of 50.

Strength & Conditioning Journal, 2016

SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) IS AN AUTOIMMUNE DISEASE AFFECTING MORE THAN 1 MILLION AMERICA... more SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) IS AN AUTOIMMUNE DISEASE AFFECTING MORE THAN 1 MILLION AMERICANS. ALTHOUGH THERE IS NO CURE, EXERCISE INTERVENTIONS CAN IMPROVE AEROBIC FITNESS AND QUALITY OF LIFE WHILE MITIGATING SOME SLE SYMPTOMS. THE LITERATURE LACKS COMPREHENSIVE EXERCISE GUIDELINES AND SPECIAL CONSIDERATIONS FOR SLE PATIENTS. HERE, WE PRESENT THE BENEFITS OF EXERCISE AND PROVIDE PRACTITIONERS AND CLINICIANS WITH EXERCISE RECOMMENDATIONS/CONSIDERATIONS FOR INDIVIDUALS WITH SLE. MOST SLE PATIENTS CAN SAFELY ENGAGE IN EXERCISE TRAINING WITH PHYSICIAN CLEARANCE, BUT CONSIDERATIONS SHOULD BE TAKEN FOR THOSE (A) WITH CARDIOPULMONARY INVOLVEMENT, (B) TAKING ANALGESICS OR CORTICOSTEROIDS, OR (C) WHO EXPERIENCE ULTRAVIOLET LIGHT EXPOSURE.

Physiology

Due to the hierarchical structure of tendon tissue (fascicles→fibers→fibrils), it is essential to... more Due to the hierarchical structure of tendon tissue (fascicles→fibers→fibrils), it is essential to investigate morphology and mechanics at the nano-scopic level to better understand whole body function. Previous studies investigating changes in tendon mechanics after exercise/disease/unloading have focused on the whole tendon and fascicle levels, but limited data exists on adaptations at the collagen fibril level. Objective: Provide a new method to study previously frozen tendon tissue by investigating collagen fibril 1) morphology, 2) nano-mechanical properties, and 3) elasticity maps using atomic force microscopy (AFM). Hypothesis: This method will provide a reliable way to assess tendon structure and function at the nano-scale. Methods: C57BL/6J mouse tendons from NASA Rodent Research-1 (-80°C) were chemically separated and mounted onto glass slides then mechanically separated into tendon subunit sheets and left to air-dry. Collagen fibril morphology was tested with a JPK Nanowiza...

Medicine and science in sports and exercise, 2016

Muscle relaxation rate is an important intrinsic contractile property that influences the neural ... more Muscle relaxation rate is an important intrinsic contractile property that influences the neural drive necessary to achieve a desired force. Most relaxation data are obtained at rest through evoked contractions; however, the application of transcranial magnetic stimulation (TMS) during a maximal voluntary contraction (MVC) allows for an in vivo (i.e., a more functionally-relevant) measurement of muscle relaxation. PURPOSE: The purpose of this study was to determine if TMS-induced relaxation is sufficiently sensitive to detect changes in plantar flexor muscle length when all synergists are actively engaged and the ankle joint angle is varied. METHODS: Seven males (24.3 ± 7.3 years; mean ± SD) performed a total of 21 brief (~3s) isometric plantar flexor MVCs in a prone position at full knee extension, randomized between 20° dorsiflexion (DF), a neutral ankle position (0°), and 30° plantar flexion (PF). During each MVC, high-intensity TMS (80% of stimulator output) was delivered to the motor cortex with a double-cone coil attached to two magnets via a BiStim unit. Peak relaxation rate was calculated to be the steepest slope of the TMSinduced drop in torque. RESULTS: MVC torque was significantly greater in the dorsiflexed (178.6 ± 35.5 Nm) compared to neutral position (144.2 ± 19.6 Nm) and in the neutral compared to plantar flexed position (59.0 ± 10.0 Nm). Peak relaxation rate was equivalent at 20° DF (-2060.3 ± 626.7 Nm/s) and 0° (-1944.8 ± 259.9 Nm/s) and both rates were significantly faster compared to the rate at 30° PF (-794.1 ± 203.9 Nm/s). CONCLUSION: Absolute relaxation rate was markedly slower when the plantar flexor muscles were placed in a shortened position, which indicates that TMS is sufficiently sensitive to detect changes in muscle length. These results support published data which demonstrate an ability of TMS to detect changes in muscle relaxation rate due to temperature, fatigue, stimulus intensity, and synergist contribution.

Strength and Conditioning Journal, May 1, 2015

The biochemist, Dec 22, 2022

Busting muscle myths Skeletal muscle is the most abundant tissue in the human body. Known for its... more Busting muscle myths Skeletal muscle is the most abundant tissue in the human body. Known for its primary role in movement, muscle also plays important roles in regulating metabolism, maintaining body temperature and providing large stores of protein, carbohydrates and fats. Muscle cells (known as 'muscle fibres') can rapidly adapt to exercise or disuse by changing size and function. Many myths and misconceptions have proliferated through the years related to skeletal muscle, exercise training and human performance. Some of these myths have spanned centuries, but more recent research has passed doubt on these stories. In this article, we address common misconceptions, including the 'go big or go home' and 'if you don't use it, you lose it' approaches to training. Clarification of these myths could positively impact individual exercise programs/therapies and their outcomes.

Access to thesis permanently restricted to Ball State community only.Access to abstract permanent... more Access to thesis permanently restricted to Ball State community only.Access to abstract permanently restricted to Ball State community only.School of Physical Education, Sport, and Exercise ScienceThesis (Ph. D.

Physiological Reports, Dec 1, 2019

In 2007 the National Institutes of Health launched the Human Microbiome Project (HMP), an interdi... more In 2007 the National Institutes of Health launched the Human Microbiome Project (HMP), an interdisciplinary research initiative seeking to characterize the contribution of human gut microbiota to health and disease (Turnbaugh et al., 2007). Subsequent findings have demonstrated compelling relationships between human gut microbiome composition and many leading causes of death worldwide including cardiovascular disease (Wang et al., 2011), diabetes (Larsen et al., 2010), and cancer (Ahn et al., 2013). Although the gut microbiome is suggested to exhibit exceptional plasticity (Gomez et al., 2019), a detailed understanding of the factors determining human microbiome assembly is lacking (Relman, 2015).

The Journal of Physiology, Jan 30, 2023

Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. ... more Most cells in the body are mononuclear whereas skeletal muscle fibres are uniquely multinuclear. The nuclei of muscle fibres (myonuclei) are usually situated peripherally which complicates the equitable distribution of gene products. Myonuclear abundance can also change under conditions such as hypertrophy and atrophy. Specialised zones in muscle fibres have different functions and thus distinct synthetic demands from myonuclei. The complex structure and regulatory requirements of multinuclear muscle cells understandably led to the hypothesis that myonuclei govern defined ‘domains’ to maintain homeostasis and facilitate adaptation. The purpose of this review is to provide historical context for the myonuclear domain and evaluate its veracity with respect to mRNA and protein distribution resulting from myonuclear transcription. We synthesise insights from past and current in vitro and in vivo genetically modified models for studying the myonuclear domain under dynamic conditions. We also cover the most contemporary knowledge on mRNA and protein transport in muscle cells. Insights from emerging technologies such as single myonuclear RNA‐sequencing further inform our discussion of the myonuclear domain. We broadly conclude: (1) the myonuclear domain can be flexible during muscle fibre growth and atrophy, (2) the mechanisms and role of myonuclear loss and motility deserve further consideration, (3) mRNA in muscle is actively transported via microtubules and locally restricted, but proteins may travel far from a myonucleus of origin and (4) myonuclear transcriptional specialisation extends beyond the classic neuromuscular and myotendinous populations. A deeper understanding of the myonuclear domain in muscle may promote effective therapies for ageing and disease. image

Medicine and Science in Sports and Exercise, May 1, 2018

Medicine and Science in Sports and Exercise, May 1, 2017

METHODS: 23 early pubertal children (16 F; 7-11 years) and 15 young adults (7 F; 21-35 years) und... more METHODS: 23 early pubertal children (16 F; 7-11 years) and 15 young adults (7 F; 21-35 years) underwent an incremental ramp exercise test on a cycle ergometer. Pulmonary gas exchange was measured breath-by-breath (Vmax, Carefusion). Vastus lateralis [HHb] was quantified by TRS-NIRS (TRS-21, Hamamatsu Photonics). RESULTS: Peak VO 2 was not different between children and adults normalized to body mass (46.7±8.1 vs. 48.9±7.7 mL/min/kg). Absolute [HHb] was not different between children and adults during unloaded pedaling (23.5±5.5 vs 26.8±10.0 uM, p=0.20) but adults had a higher peak exercise [HHb] (32.0±8.2 vs 44.4±22.6 uM, p=0.01). Two way RM-ANOVA of relative HHb dynamics revealed an effect of age (F(1,36) = 6.895, p=0.013) and interaction with % peak power (p=0.001, Figure). Post-hoc, relative HHb was lower at 60% peak power in children vs adults (57±10% vs 68±13%, p=0.0006), while VO 2 did not differ (33.5±4.9% vs 30.6±6.2%, p=0.12). CONCLUSION: Muscle deoxygenation is both attenuated and delayed during incremental exercise in children compared to adults, despite similar relative VO 2. This is consistent with a closer matching of muscle microvascular O 2 delivery to utilization over a greater range of aerobic power in children. The mechanisms contributing to this improved regulation of muscle blood flow during exercise in children warrant further study.

Background: Metabolic carts measure the carbon dioxide (CO 2) produced and oxygen consumed by an ... more Background: Metabolic carts measure the carbon dioxide (CO 2) produced and oxygen consumed by an individual when breathing to assess metabolic fuel usage (carbohydrates versus fats). However, these systems are expensive, time-consuming, and only available in health care laboratory settings. A small handheld device capable of determining metabolic fuel usage via CO 2 from exhaled air has been developed. Objective: The aim of this study is to evaluate the validity of a novel handheld device (Lumen) for measuring metabolic fuel utilization in healthy young adults. Methods: Metabolic fuel usage was assessed in healthy participants (n=33; mean age 23.1 years, SD 3.9 years) via respiratory exchange ratio (RER) values obtained from a metabolic cart as well as % CO 2 from the Lumen device. Measurements were performed at rest in two conditions: fasting, and after consuming 150 grams of glucose, in order to determine changes in metabolic fuel usage. Reduced major axis regression and simple linear regression were performed to test for agreement between RER and Lumen % CO 2. Results: Both RER and Lumen % CO 2 significantly increased after glucose intake (P<.001 for both) compared with fasting conditions, by 0.089 and 0.28, respectively. Regression analyses revealed an agreement between the two measurements (F 1,63 =18.54; P<.001). Conclusions: This study shows the validity of Lumen for detecting changes in metabolic fuel utilization in a comparable manner with a laboratory standard metabolic cart, providing the ability for real-time metabolic information for users under any circumstances.

Frontiers in rehabilitation sciences, Aug 8, 2022

Background: Virtual exercise has become more common as emerging and converging technologies make ... more Background: Virtual exercise has become more common as emerging and converging technologies make active virtual reality games (AVRGs) a viable mode of exercise for health and fitness. Our lab has previously shown that AVRGs can elicit moderate to vigorous exercise intensities that meet recommended health benefit guidelines. Dissociative attentional focuses during AVRG gameplay have the potential to widen the gap between participants' perception of exertion and actual exertion. Objective: The aim of this study was to determine actual exertion (AEx) vs. perceived exertion (PEx) levels during AVRGs by measuring heart rate (HR) and ratings of perceived exertion (RPE) in two di erent settings. Materials and methods: HR and RPE were collected on participants (N = ; age. ± .) during min of gameplay in LabS and GymS using the HTC VIVE with the following games played: Fruit Ninja VR (FNVR), Beat Saber (BS), and Holopoint (HP). Results: Participants exhibited significantly higher levels of AEx compared to reported PEx for all three AVRGs (Intensity): FNVR [AEx =. ±. (Light), PEx =. ±. (Very Light)], BS [AEx =. ±. (Light), PEx =. ±. (Very Light)], HP [AEx =. ±. (Somewhat Hard), PEx =. ±. (Light-Somewhat Hard)]. Additionally, participants playing in the GymS experienced significantly higher levels of AEx [. ±. (Light-Somewhat Hard)] and PEx [. ±. (Very Light-Light)] compared to the LabS [AEx =. ±. (Light), PEx =. ±. (Very Light-Light)]. Conclusion: Perceptions of exertion may be lower than actual exertion during AVRG gameplay, and exertion levels can be influenced by the setting in which AVRGs are played. This may inform VR developers and health clinicians who aim to incorporate exercise/fitness regimens into upcoming 'virtual worlds' currently being developed at large scales (i.e., the "metaverse").

Strength and Conditioning Journal, Dec 1, 2016

Medicine & Science in Sports & Exercise, 2020

210 Board #26 May 27 9:30 AM 11:00 AM Effect Of Exercise Setting On Energy Expenditure And Enjoym... more 210 Board #26 May 27 9:30 AM 11:00 AM Effect Of Exercise Setting On Energy Expenditure And Enjoyment During Active Virtual Reality Gaming Trenton Huynh Stewart, Kirsten Villanueva, Amanda Hahn, Julissa Ortiz, Chandler Wolf, Randy Nguyen, Nicole D. Bolter, Marialice Kern, FACSM, James R. Bagley. San Francisco State University, San Francisco, CA. (Sponsor: Marilice Kern, FACSM) Email: tstewar1@sfsu.edu

Medicine & Science in Sports & Exercise, 2020

BackgroundMetabolic carts measure the carbon dioxide produced and oxygen consumed from the breath... more BackgroundMetabolic carts measure the carbon dioxide produced and oxygen consumed from the breath in order to assess metabolic fuel usage (carbohydrates vs. fats). However, these systems are expensive, time-consuming, and only available in the clinic. A small hand-held device capable of measuring metabolic fuel via CO2from exhaled air has been developedObjectiveTo evaluate the validity of a novel hand-held device (Lumen®) for measuring metabolic fuel utilization in healthy young adultsMethodsMetabolic fuel usage was assessed in healthy participants (n = 33; age: 23.1 ± 3.9 y) via respiratory exchange ratio (RER) values from the “gold-standard” metabolic cart as well as %CO2from the Lumen device. Measurements were performed at rest in two conditions, fasting, and after consuming 150 grams of glucose in order to determine changes in metabolic fuel. Reduced major axis regression was performed as well as Bland-Altman plots and linear regressions to test for agreement between RER and Lum...

Medicine & Science in Sports & Exercise, 2017

Medicine & Science in Sports & Exercise, 2017

PURPOSE: Bioelectrical impedance analysis (BIA) scales have gained popularly in monitoring fitnes... more PURPOSE: Bioelectrical impedance analysis (BIA) scales have gained popularly in monitoring fitness progress at home, yet their accuracy is unknown. We assessed the validity and reliability of body fat percentage (BF%) measurements from a consumer bioelectrical analysis (cBIA) scale compared to the “gold standard” of hydrostatic weighing (HW). METHODS: Forty-three [male (n=22); female (n=21)] healthy volunteers [age: 27.9±5.6y; height: 170.0±8.6cm; mass: 69.0±13.7kg; body mass index (BMI) range: 16.8-33.1] arrived at the laboratory 3h fasted after 12h without exercise and underwent measures of residual lung volume (for HW calculations), hydration status, and BF% via cBIA scale (‘Lean’ and ‘Regular’ modes) and HW. We assessed cBIA scale validity using Bland-Altman Plots (identifying Mean Biases±Limits of Agreement) and reliability using intraclass correlation coefficients (ICC). RESULTS: With HW as the validity criterion, mean BF% was 22.3±6.1% for all participants (range: 5.3-35.8%; male mean: 20.8±6.4%; female mean: 23.9±5.5%). Compared to HW, the cBIA scale in ‘Lean’ mode underestimated BF% by -5.3±9.1% for all participants (males: -7.9±6.9%; females: -2.6±8.0%) (p≤0.05). In ‘Regular’ mode, the cBIA scale agreed with HW for all participants (BF% -0.8±9.3%; p=0.27) and females (BF% 0.4±10.8%; p=0.73); however, there was a significant difference for males (BF% 2.0±7.1%; p≤0.05). The cBIA was reliable when comparing day-to-day (‘Lean’ mode: 0.5±1.0%, ICC:0.99; ‘Regular’ mode: 0.4±1.0%, ICC:0.99) and week-to-week (‘Lean’ mode: -0.4±1.4%, ICC:0.98; ‘Regular’ mode: -0.2±1.5%, ICC:0.97) BF% for all participants. CONCLUSIONS: Compared to HW, the cBIA underestimated BF% in ‘Lean’ mode, and this discrepancy was more pronounced in males. However, the cBIA scale agreed with HW when analyzing BF% in ‘Regular’ mode for all participants and females, signifying the “mode” chosen on consumer BIA devices greatly impacts validity. The cBIA was reliable when comparing day-to-day and week-to-week BF% measures for all participants, suggesting this can be a reliable at-home BF% analysis scale.

Medicine & Science in Sports & Exercise, 2016

We caused myocardial infarction via ligation of the left anterior descending coronary artery to i... more We caused myocardial infarction via ligation of the left anterior descending coronary artery to induce CHF in mice, while sham animals received identical surgical procedures except ligation. We performed experiments 14-16 weeks post-surgery, and tested contractile properties of permeabilized diaphragm single fibers with or without exposure to the thiol-reducing agent dithiothreitol (DTT, 10 mM for 10min) prior to calcium activation. RESULTS: Maximal specific force (sFo) of diaphragm fibers was decreased in CHF compared to sham (in kN•m-2, 132.3 ±6.5 and 96.9 ±6.0), and sFo of fibers from CHF mice was increased by DTT treatment (126.3 ±6.6 kN•m-2). The rate constant of tension redevelopment (Ktr) was slower in CHF diaphragm fibers than sham (in s-1 44.12 ±3.9 and 31.26 ±2.4), and DTT treatment increased Ktr (41.4 ±1.7 s-1). Calcium sensitivity was unchanged by either CHF or DTT treatment. DTT had no effect on the single fiber contractile parameters (sFo, Ktr and pCa50) in sham animals. CONCLUSIONS: Our findings suggest that reversible thiol oxidation of sarcomeric proteins is a molecular mechanism of diaphragm fiber contractile dysfunction in CHF.

Isokinetics and Exercise Science, 2016

BACKGROUND: Anaerobic fatigue is a limiting factor in performance and athletes are often tested t... more BACKGROUND: Anaerobic fatigue is a limiting factor in performance and athletes are often tested to determine their fatigue resistance. Administering the classic Thorstensson test of fatigability is a popular method to determine fatigue percentage as it requires 50 maximal knee extension repetitions. However, there has been little research to determine whether performing more or fewer repetitions yields similar results. OBJECTIVE: The purpose of this study was to compare concentric fatigue percentage (FP) between the classic Thorstensson test (CT; average of first 3 repetitions to average of last 3 repetitions) and three different repetition ranges: peak torque repetition to repetition 30 (P30), peak torque repetition to repetition 50 (P50), and peak torque repetition to repetition 60 (P60). METHODS: Fifteen resistance trained men (age = 24.8 ± 1.3 yrs; height = 178.9 ± 5.1 cm; mass = 82.2 ± 8.0 kg) volunteered to perform 60 maximal concentric knee extension repetitions at 180 • /s on an isokinetic dynamometer, measuring peak torque of each repetition. RESULTS: P30 (r = 0.81) and P50 (r = 0.77) were highly correlated with CT but P60 (r = 0.58) was only moderately correlated with CT. P30 FP (44.7 ± 8.8) was significantly less than CT (62.3 ± 6.0), P50 (66.0 ± 6.8) and P60 (69.7 ± 7.1). CONCLUSION: FP can be determined through fewer repetitions of a knee extension fatigue test on an isokinetic dynamometer. While both P30 and P50 were highly correlated with CT, performing fewer repetitions requires less time to complete as well as less residual fatigue. When measuring knee extension FP, the number of repetitions performed in the test may be reduced to 30 while still maintaining a high correlation to a longer method of 50.

Strength & Conditioning Journal, 2016

SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) IS AN AUTOIMMUNE DISEASE AFFECTING MORE THAN 1 MILLION AMERICA... more SYSTEMIC LUPUS ERYTHEMATOSUS (SLE) IS AN AUTOIMMUNE DISEASE AFFECTING MORE THAN 1 MILLION AMERICANS. ALTHOUGH THERE IS NO CURE, EXERCISE INTERVENTIONS CAN IMPROVE AEROBIC FITNESS AND QUALITY OF LIFE WHILE MITIGATING SOME SLE SYMPTOMS. THE LITERATURE LACKS COMPREHENSIVE EXERCISE GUIDELINES AND SPECIAL CONSIDERATIONS FOR SLE PATIENTS. HERE, WE PRESENT THE BENEFITS OF EXERCISE AND PROVIDE PRACTITIONERS AND CLINICIANS WITH EXERCISE RECOMMENDATIONS/CONSIDERATIONS FOR INDIVIDUALS WITH SLE. MOST SLE PATIENTS CAN SAFELY ENGAGE IN EXERCISE TRAINING WITH PHYSICIAN CLEARANCE, BUT CONSIDERATIONS SHOULD BE TAKEN FOR THOSE (A) WITH CARDIOPULMONARY INVOLVEMENT, (B) TAKING ANALGESICS OR CORTICOSTEROIDS, OR (C) WHO EXPERIENCE ULTRAVIOLET LIGHT EXPOSURE.

Physiology

Due to the hierarchical structure of tendon tissue (fascicles→fibers→fibrils), it is essential to... more Due to the hierarchical structure of tendon tissue (fascicles→fibers→fibrils), it is essential to investigate morphology and mechanics at the nano-scopic level to better understand whole body function. Previous studies investigating changes in tendon mechanics after exercise/disease/unloading have focused on the whole tendon and fascicle levels, but limited data exists on adaptations at the collagen fibril level. Objective: Provide a new method to study previously frozen tendon tissue by investigating collagen fibril 1) morphology, 2) nano-mechanical properties, and 3) elasticity maps using atomic force microscopy (AFM). Hypothesis: This method will provide a reliable way to assess tendon structure and function at the nano-scale. Methods: C57BL/6J mouse tendons from NASA Rodent Research-1 (-80°C) were chemically separated and mounted onto glass slides then mechanically separated into tendon subunit sheets and left to air-dry. Collagen fibril morphology was tested with a JPK Nanowiza...

Medicine and science in sports and exercise, 2016

Muscle relaxation rate is an important intrinsic contractile property that influences the neural ... more Muscle relaxation rate is an important intrinsic contractile property that influences the neural drive necessary to achieve a desired force. Most relaxation data are obtained at rest through evoked contractions; however, the application of transcranial magnetic stimulation (TMS) during a maximal voluntary contraction (MVC) allows for an in vivo (i.e., a more functionally-relevant) measurement of muscle relaxation. PURPOSE: The purpose of this study was to determine if TMS-induced relaxation is sufficiently sensitive to detect changes in plantar flexor muscle length when all synergists are actively engaged and the ankle joint angle is varied. METHODS: Seven males (24.3 ± 7.3 years; mean ± SD) performed a total of 21 brief (~3s) isometric plantar flexor MVCs in a prone position at full knee extension, randomized between 20° dorsiflexion (DF), a neutral ankle position (0°), and 30° plantar flexion (PF). During each MVC, high-intensity TMS (80% of stimulator output) was delivered to the motor cortex with a double-cone coil attached to two magnets via a BiStim unit. Peak relaxation rate was calculated to be the steepest slope of the TMSinduced drop in torque. RESULTS: MVC torque was significantly greater in the dorsiflexed (178.6 ± 35.5 Nm) compared to neutral position (144.2 ± 19.6 Nm) and in the neutral compared to plantar flexed position (59.0 ± 10.0 Nm). Peak relaxation rate was equivalent at 20° DF (-2060.3 ± 626.7 Nm/s) and 0° (-1944.8 ± 259.9 Nm/s) and both rates were significantly faster compared to the rate at 30° PF (-794.1 ± 203.9 Nm/s). CONCLUSION: Absolute relaxation rate was markedly slower when the plantar flexor muscles were placed in a shortened position, which indicates that TMS is sufficiently sensitive to detect changes in muscle length. These results support published data which demonstrate an ability of TMS to detect changes in muscle relaxation rate due to temperature, fatigue, stimulus intensity, and synergist contribution.