Michael R. Deschenes

William & Mary | WM · Department of Kinesiology and Health Sciences

This study tests the effect of trimetazidine dihydrochloride (TMZ) on contractility in fast and slow skeletal muscles of adult (Ad, 6-8 mo.) and aged (Ag, 75% lifespan) male (M) and female (F) F344/BN rats. We hypothesized that TMZ would enhance contractility produced by indirect, but not direct, stimulation. Methods: Rats were injected with 3 mg/k...

The neuromuscular system accounts for a large portion (~40%) of whole body mass while enabling body movement, including physical work and exercise. At the core of this system is the neuromuscular junction (NMJ) which is the vital synapse transducing electrical impulses from the motor neurons to their post-synaptic myofibers. Recent findings suggest...

Background: Injection of exogenous mitochondria has been shown to improve the ischaemia-damaged myocardium, but the effect of mitochondrial transplant therapy (MTT) to restore skeletal muscle mass and function has not been tested following neuromuscular injury. Therefore, we tested the hypothesis that MTT would improve the restoration of muscle fu...

This study aimed to describe changes in forelimb grip strength and ex vivo muscle force production in adult (Ad) and aged (Ag, 75% lifespan) male (M) and female (F) F344/BN hybrid rats. We hypothesized that differences in M vs. F would be explained by muscle mass, but that age differences would persist after normalizing to mass in fast, but not slo...

Aging is associated with gradual degeneration, in mass and function, of the neuromuscular system. This process, referred to as “sarcopenia”, is considered a disease by itself, and it has been linked to a number of other serious maladies such as type II diabetes, osteoporosis, arthritis, cardiovascular disease, and even dementia. While the molecular...

Muscle unloading results in severe disturbance in neuromuscular function. During juvenile stages of natural development, the neuromuscular system experiences a high degree of plasticity in function and structure. This study aimed to determine whether muscle unloading imposed during juvenile development would elicit more severe disruption in neuromu...

Introduction/Aims Muscle unloading imparts subtotal disuse on the neuromuscular system resulting in reduced performance capacity. This loss of function, at least in part, can be attributed to disruptions at the neuromuscular junction (NMJ). However, research has failed to document morphological remodeling of the NMJ with short term muscle unloading...

The neuromuscular junction (NMJ) is the synapse joining the motor neuron with the myofiber(s) that are innervated by an excitatory neuron, enabling the proper function of the neuromuscular system. Since sarcopenia is currently defined mainly by age-related declines in muscle function, rather than mass, the importance of understanding age-related de...

The neuromuscular junction (NMJ) connects the motor neuron with myofibers allowing muscle contraction. Both aging and increased activity result in NMJ remodeling. Here, the effects of exercise were examined in young and aged soleus muscles. Using immunofluorescent staining procedures, cellular and active zone components of the NMJ were quantified f...

It is known that both exercise and aging influence neuromuscular performance; however their effects on post-exercise recovery are largely unknown. To examine how exercise training and aging might affect post-exercise recovery, the function of muscles taken from young, and aged male rats assigned to exercise, or control conditions was assessed with...

The neuromuscular junction (NMJ) is the synapse that enables proper function of the neuromuscular system. Like other synapses, the NMJ is sensitive to changes in its pattern of use and adapts accordingly. Exercise training stimulates the NMJ and elicits functional and morphological remodeling resulting in improved performance. Physiologically, exer...

Background: This project aimed to determine the adaptability of the neuromuscular system to the stimuli of exercise training, and aging. Methods: Young adult, and aged male rats were randomly assigned to either exercise training, or sedentary control groups. Exercise training featured an 8 week program of treadmill running. At the end of the int...

Previously, it has been shown that following muscle unloading, males and females experience different maladaptations in neuromuscular function. As a follow-up, the present investigation sought to determine if male and female neuromuscular systems demonstrated similar, or disparate morphological adaptations to muscle unloading. Twenty young adult ma...

Objective: The aim of this study was to assess the efficacy of long-term resistance training in preventing the detrimental effects of muscle unloading on neuromuscular function. Design: Eleven untrained men and 11 men with extensive backgrounds in resistance training were tested for several parameters of neuromuscular function at various isokine...

Volumetric muscle loss (VML) can result from trauma, infection, congenital anomalies, or surgery, and produce permanent functional and cosmetic deficits. There are no effective treatment options for VML injuries, and recent advances toward development of muscle constructs lack the ability to achieve innervation necessary for long-term function. We...

Purpose of review: Denervation is a hallmark of age-related and other types of muscle wasting. This review focuses on recent insights and current viewpoints regarding the mechanisms and clinical relevance of maintaining the neuromuscular junction to counteract muscle wasting resulting from aging or neural disease/damage. Recent findings: Activit...

Introduction: The potential of gender to affect unloading-induced neuromuscular adaptations was investigated. Methods: Twenty male and 20 female rats were assigned to control (CTL), or unloaded (UL) conditions. After 2 weeks of unloading, soleus muscles were removed, and neuromuscular function was assessed during a train of alternating indirect...

The objective of this study was to determine whether pre- to post-synaptic coupling of the neuromuscular junction (NMJ) could be maintained in the face of significant morphological remodeling brought about by exercise training, and whether aging altered this capacity. Eighteen young adult (8 mo) and eighteen aged (24 mo) Fischer 344 rats were rando...

Help your students develop an understanding of exercise physiology concepts and their application athletic performance and well-being with Exercise Physiology, 2e. Using an engaging evidence-based approach that combines research and theory with practical discussions of nutrition and training, the authors help students understand how the human body...

To examine the effects of aging on neuromuscular adaptations to resistance training (i.e., weight lifting), young (9 months of age) and aged (20 months of age) male rats either participated in a 7-week ladder climbing protocol with additional weight attached to their tails or served as controls (n = 10/group). At the conclusion, rats were euthanize...

Functional denervation is a hallmark of aging sarcopenia as well as of muscular dystrophy. It is thought to be a major factor reducing skeletal muscle mass, particularly in the case of sarcopenia. Neuromuscular junctions (NMJs) serve as the interface between the nervous and skeletal muscular systems, and thus they may receive pathophysiological inp...

Sarcopenia, or the age-related loss of muscle size/mass, is a major health concern in western societies where aging is prevalent. Currently, more is known about sarcopenia's impact on health and quality of life, than its physiological etiology. It remains to be clearly determined whether the onset and progression of sarcopenia is similar throughout...

The neuromuscular junction (NMJ) displays considerable morphological plasticity as a result of differences in activity level, as well as aging. This is true of both pre-synaptic and post-synaptic components of the NMJ. Yet, despite these variations in NMJ structure, proper pre- to post-synaptic coupling must be maintained in order for effective cel...

Objectives: Both sex and aging have been shown to affect physiological responses to exercise. The aim of the present investigation was to determine whether aging impacted the sex-specific nature of physiological responses to exercise commonly noted among young adults. Methods: Ten aged men (69.0 ± 1.7 years; mean ± SE) and 10 aged women (71.6 ±...

This investigation aimed to: (1) confirm whether women were more vulnerable to the negative neuromuscular adaptations elicited by muscle unloading and if so, (2) determine which physiological mechanism(s) explain those gender-related differences. Healthy young men (20.7 ± 0.3 years) and women (20.3 ± 0.3 years)-(N = 12/group)-participated by comple...

The capacity of pre-habilitative conditioning - exercise performed a priori - to mitigate neuromuscular maladaptations to disuse is unclear. This study evaluated pre-habilitation by examining neuromuscular junctions (NMJs) and the myofibers they innervate in young adult and aged muscles. Within each age category, 40 rats were divided into four trea...

The purpose of this Position Stand is to provide guidance to professionals who counsel and prescribe individualized exercise to apparently healthy adults of all ages. These recommendations also may apply to adults with certain chronic diseases or disabilities, when appropriately evaluated and advised by a health professional. This document supersed...

This investigation sought to determine if aging affected adaptations of the neuromuscular junction (NMJ) to exercise training. Twenty young adult (8 months) and 20 aged (24 months) rats were assigned to either a program of treadmill exercise, or sedentary conditions. Following the 10-week experimental period, rats were euthanized, and soleus and pl...

The neuromuscular system is one of the largest and most vital organ systems of the body. The function and mass of the neuromuscular system gradually deteriorate during the natural process of aging. The neuromuscular system is comprised of individual motor units, each of which features a single motor neuron and all the muscle fibers it innervates. M...

Several mechanisms contributing to the etiology of sarcopenia (age-related loss of muscle size) have been postulated. One of these attributes the loss of muscle mass to a preceding age-related denervation of myofibers. The aim of this study was to determine if signs of denervation were apparent at the neuromuscular junction (NMJ) before fiber atrop...

Previously, we have examined how aging affects the physiological responses of men to endurance exercise. In the present investigation, we aimed to extend our assessment of the influence of aging on exercise-induced responses by focusing on women. Ten young (20.3 +/- 0.3 years; mean +/- SE) and 10 aged (75.5 +/- 1.2 years) women performed 30 min of...

Muscle unloading results in decreased strength. This is partly attributed to reduced neural activation. This study examined whether men and women experienced different adaptations to muscle unloading. Ten men (21.4 +/- 0.8 years; mean +/- SE) and ten women (20.9 +/- 0.2 years) were subjected to 1 week of muscle unloading. Muscle function was quanti...

Unlike skeletal muscle, the effect of aging on training induced adaptations of the neuromuscular junction (NMJ) has received scant attention. This study aimed to determine whether this important synapse exhibits age‐specific adaptations to endurance training. Twenty young adult (8 mo) and 20 aged (24 mo) male Fischer 344 rats were assigned to eithe...

It has been well documented that muscle unloading elicits significant decrements in muscle strength and size. In contrast, the effects of muscle unloading on the neuromuscular junction (NMJ) are less elucidated and the potential of pre‐habilitative conditioning remains unknown. The aim of this study was to examine the impact of unloading on the NMJ...

To determine whether prehabilitation, or exercise performed before muscle unloading, can effectively mitigate decreases in neuromuscular function typically elicited by unloading. Ten healthy, untrained young men (20.9 +/- 1.3 yrs; mean +/- SD) were initially tested for strength, work, power, and electromyography. After completing six prehabilitativ...

The purpose of this investigation was to determine whether young (21.7 yr) and aged (68.5 yr) men experienced similar responses to 7 d of muscle unloading (N = 10 per group). Unilateral lower limb suspension (ULLS) was used to impose muscle unloading of the knee extensors. To compare the effects of unloading on aged and young men, a repeated-measur...

Previous studies indicate a link between caloric restriction, SIRT1 expression, and longevity. It has been suggested that the metabolic stress of exercise may also alter SIRT1 expression. Therefore, we evaluated the effects of two different modes of exercise training on myocardial SIRT1 protein expression in young and old rats. In the first study,...

Sarcopenia has been linked to a host of health problems including osteoporosis, accidental falls, and type II diabetes. Denervation may precipitate the loss in muscle size and change in fiber type distribution characterizing sarcopenia. This study aimed to determine whether remodeling of the neuromuscular junction (NMJ) preceded alterations in myof...

The aim of this study was to determine the impact of resistance exercise on neuromuscular junction (NMJ) architecture. Eighteen Sprague-Dawley rats either participated in a 7-week resistance training program or served as untrained controls. Following the experimental period, the NMJs of soleus muscles were visualized with immunofluorescent techniqu...

Introduction and general principlesHormone categorization and synthesisRegulation of hormone secretionHormone transport in the bloodMetabolic clearance of hormonesMechanism of action at target cellsIntegration of target cell responses to hormonesConcluding commentsReferences

The purpose of this investigation was to determine the effect of aging on neuromuscular adaptations to chronic overload. Eight young adult (8 months old) and eight aged (22 months old) Fischer 344 rats underwent unilateral synergist ablation to overload the plantaris and soleus muscles of that hindlimb and to provide control muscles from the contra...

The purpose of this investigation was to determine the effects of 3 wk of L-carnitine L-tartrate (LCLT) supplementation and post-resistance-exercise (RE) feeding on hormonal and androgen receptor (AR) responses. Ten resistance-trained men (mean+/-SD: age, 22+/-1 yr; mass, 86.3+/-15.3 kg; height, 181+/-11 cm) supplemented with LCLT (equivalent to 2...

This investigation was conducted to compare the physiological responses of men and women, both during and following an exercise bout at the same relative submaximal intensity. Ten untrained men (20.7+/-0.5 yr, 178.4+/-2.3 cm, 79.6+/-4.8 kg; mean+/-SE) and 10 untrained women (20.3+/-0.3 yr, 163.8+/-2.2 cm, 59.5+/-2.1 kg) cycled for 30 min at 60-65%...

The purpose of this study was to examine pituitary-adrenal (PA) hormone responses [beta-endorphin (beta-END), adrenocorticotropic hormone (ACTH) and cortisol] to arm exercise (AE) and leg exercise (LE) at 60 and 80% of the muscle-group specific VO2 peak. Eight healthy untrained men (AE VO2 peak=32.4+/-3.0 ml kg(-1) min(-1), LE VO2 peak=46.9+/-5.3 m...

Physiological responses to exercise of moderate intensity and duration among aged compared to young adults have yet to be clearly defined. Further, the effects of aging on the rate and effectiveness of postexercise recovery are unknown. Here, selected physiological responses during and following exercise of the same relative intensity were examined...

The objective of this investigation was to compare the effects of decreased vs. increased activity on the neuromuscular system. Twenty-four young adult (7 weeks old) Sprague-Dawley rats were randomly assigned to three treatment groups (N=8/group). Increased activity was achieved by treadmill running for up to 1 h/day. Decreased activity was induced...

The neuromuscular junction (NMJ) allows communication between motor neurons and muscle fibers. During development, marked morphological changes occur as the functional NMJ is formed. During the postnatal period of rapid growth and muscle enlargement, endplate size concurrently increases. Even beyond this period of pronounced plasticity, the NMJ und...

The effects of microgravity were determined in muscles of differing function and myofiber-type composition. Rats were assigned either to a 10-day spaceflight mission or to ground-based control conditions. Following the experimental period, hindlimb muscles were obtained from both groups. Cytofluorescent techniques were used to examine neuromuscular...

The purpose of the present investigation was to examine androgen receptor (AR) content in the vastus lateralis following two resistance exercise protocols of different volume. Nine resistance-trained men (age=24.3+/-4.4 years) performed the squat exercise for 1 (SS) and 6 sets (MS) of 10 repetitions in a random, counter-balanced order. Muscle biops...

The purpose of the present investigation was to examine androgen receptor (AR) content in the vastus lateralis following two resistance exercise protocols of different volume. Nine resistance-trained men (age=24.3±4.4 years) performed the squat exercise for 1 (SS) and 6 sets (MS) of 10 repetitions in a random, counter-balanced order. Muscle biopsie...

. Proenkephalin peptide F [107-140] is related to the enhancement of immune function, while microgravity has been shown to cause immuno-suppression. We investigated the physiological response of proenkephalin peptide F to microgravity. There were 12 Fischer 344 female rats, ovariectomized at 10.5 wk of age, used to determine plasma concentrations o...

Aging has been associated with a loss of muscle mass that is referred to as 'sarcopenia'. This decrease in muscle tissue begins around the age of 50 years, but becomes more dramatic beyond the 60th year of life. Loss of muscle mass among the aged directly results in diminished muscle function. Decreased strength and power contribute to the high inc...

The objective of the present investigation was to determine the effects of muscle unloading-a form of subtotal disuse- on the morphology of the neuromuscular junction (NMJ) in younger and aged animals. Sixteen aged (22 months) and 16 young adult (8 months) male Fischer 344 rats were assigned to control and hindlimb suspension (HS) conditions (n=8/g...

This study assessed the effect of muscle unloading on the neuromuscular system. Sixteen male Fischer 344 rats were randomly assigned to either a hindlimb suspension (unloaded) or control group (N=8/group) for 16 days. Following this intervention period, pre- and postsynaptic features of the neuromuscular junctions (NMJs) of soleus muscles were stai...

Weight lifting, or resistance training, is a potent stimulus to the neuromuscular system. Depending on the specific program design, resistance training can enhance strength, power, or local muscular endurance. These improvements in performance are directly related to the physiologic adaptations elicited through prolonged resistance training. Optima...

Previous research has indicated that 50 fiber measurements per individual for type I and II fibers would be sufficient to characterize the fiber areas. This study replicated the work of McCall et al. (1998) using the three major fiber types (I, IIA, and IIB) and sampling larger populations of fibers. Random blocks of fibers were also examined to in...

Aging is known to disrupt the "biological clock" that governs physiological variables at rest. This study sought to determine whether aged men demonstrated biorhythmic variation in muscle performance during resistance exercise and physiological responses to that stimulus. Ten aged (75.6 +/- 1.6 yr; mean +/- SE) men completed an isokinetic testing p...

Strength decrements observed after extended (4-6 wk) periods of muscle unloading are associated with significant atrophy. Because early (up to 2 wk) strength gains from resistance exercise are related to improved neural recruitment, we hypothesized that the loss of strength resulting from 2 wk of muscle unloading [unilateral lower limb suspension (...

It has previously been established that spaceflight elicits alterations in the morphology of the neuromuscular system that includes expansion of the neuromuscular junction (NMJ) and myofiber atrophy. The purpose of this study was to determine the capacity of the neuromuscular system to recover from spaceflight-induced modifications upon return to n...

The objective of this investigation was to determine whether morphological adaptations to unloading are different in young adult and aged skeletal muscle. Sixteen young adult (8-month) Fischer 344 rats were randomly assigned to either a control or hindlimb suspension (HS) group. Sixteen aged (22-month) rats were similarly assigned to either control...

On different days, 10 men performed 30-min sessions of cycling at 50-55% of their peak oxygen uptake (VO(2)); one at 40 rpm and another at 80 rpm. Rectal temperature, heart rate (HR), mean arterial pressure (MAP), plasma lactate, glucose, insulin, and cortisol were measured before exercise, during the 15th and 30th min of exercise, and at 5 and 10...

The aim of this study was to determine the impact of resistance exercise on neuromuscular junction (NMJ) architecture. Eighteen Sprague-Dawley rats either participated in a 7-week resistance training program or served as untrained controls. Following the experimental period, the NMJs of soleus muscles were visualized with immunofluorescent techniqu...

This study examined the biochemical, immunological, functional, and neuromuscular responses associated with exercise-induced muscle damage in the quadriceps of untrained men. Muscle damage and soreness was elicited with maximal concentric/eccentric muscle actions at 0.53 rads s(-1). Significant (P<0.05) soreness was evident 1, 2, and 3 days followi...

This study was conducted to determine whether exercise-induced improvements in capillarity in muscle with peripheral arterial insufficiency (PAI) was accompanied by endothelial cell mitosis, and whether that response could be explained by changes in the expression of basic fibroblast growth factor (bFGF), a known mitogen. After bilateral ligation o...

Previously, this laboratory has demonstrated that exhaustive aerobic exercise performance is not subject to significant chronobiological variation between 0800 and 2000 h, but certain physiological responses to maximal aerobic effort do fluctuate significantly within that time frame. The purpose of the present investigation was to determine whether...

Previous studies investigating the impact of circadian rhythms on physiological variables during exercise have yielded conflicting results. The purpose of the present investigation was to examine maximal aerobic exercise performance, as well as the physiological and psychophysiological responses to exercise, at four different intervals (0800 hours,...

Denervation elicits profound alterations in the morphometry of skeletal muscle. These alterations include changes in fiber type composition as well as reductions in fiber size. There is evidence that the increased mechanical load placed upon muscle via rhythmic stretching attenuates denervation induced alterations in muscle morphology. The purpose...

The potential for exogenous infusion of basic fibroblast growth factor (bFGF) to increase collateral blood flow to dependent tissue was quantified in adult male rats with peripheral arterial insufficiency. Occlusion of the femoral artery at a proximal site did not infringe on resting blood flow to the distal hindlimb muscle, but did remove the bloo...

The biochemical adaptations of different muscle fiber types to endurance training of various intensities and durations have previously been investigated. The objective of this study was to determine the effects of two different endurance training programs on muscle fiber morphology. Twenty-four male Sprague-Dawley rats were randomly assigned to thr...