51
|
Abstract
Patients with stroke are severely deconditioned, leading to metabolic abnormalities that significantly increase risk for myocardial infarction and recurrent stroke. This review characterizes the nature of the metabolic decline, the underlying causes, and the potential for progressive aerobic exercise to address metabolic impairment following disabling stroke. Although exercise training has previously been shown to improve peak aerobic capacity and sensorimotor function after stroke, establishing safe and effective exercise programs in this population presents unique challenges stemming from neurological deficit complexities and comorbid conditions. Thus, recommendations for application to practice are provided that include proper preexercise evaluation, guidelines for symptom-limited maximal effort exercise testing, as well as evidence-based suggestions for initiation and progression of an exercise program. Implementing regular, progressive exercise therapy is critical on the basis of the devastating impact of physical inactivity on overall metabolic heath. Prevalence of impaired or diabetic glucose metabolism may be as high as 80% in chronic stroke, predicting 2- and 3-fold increased risk for recurrent stroke, respectively. Tragically, nearly one third of patients with stroke experience recurrent stroke within 5 years, and comorbid cardiovascular conditions represent the leading cause of death in this population. Recent evidence showing the positive impact of exercise training on hyperinsulinemia and glucose tolerance in survivors of stroke is presented, given the central importance of these factors to overall cardiovascular risk. On the basis of these and other findings, structured exercise programs should be considered for all survivors of stroke.
Collapse
|
52
|
Hafer-Macko CE, Ryan AS, Ivey FM, Macko RF. Skeletal muscle changes after hemiparetic stroke and potential beneficial effects of exercise intervention strategies. JOURNAL OF REHABILITATION RESEARCH AND DEVELOPMENT 2008; 45:261-72. [PMID: 18566944 PMCID: PMC2978978 DOI: 10.1682/jrrd.2007.02.0040] [Citation(s) in RCA: 134] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Stroke is the leading cause of disability in the United States. New evidence reveals significant structural and metabolic changes in skeletal muscle after stroke. Muscle alterations include gross atrophy and shift to fast myosin heavy chain in the hemiparetic (contralateral) leg muscle; both are related to gait deficit severity. The underlying molecular mechanisms of this atrophy and muscle phenotype shift are not known. Inflammatory markers are also present in contralateral leg muscle after stroke. Individuals with stroke have a high prevalence of insulin resistance and diabetes. Skeletal muscle is a major site for insulin-glucose metabolism. Increasing evidence suggests that inflammatory pathway activation and oxidative injury could lead to wasting, altered function, and impaired insulin action in skeletal muscle. The health benefits of exercise in disabled populations have now been recognized. Aerobic exercise improves fitness, strength, and ambulatory performance in subjects with chronic stroke. Therapeutic exercise may modify or reverse skeletal muscle abnormalities.
Collapse
|
53
|
Campanini I, Merlo A, Farina D. Motor unit discharge pattern and conduction velocity in patients with upper motor neuron syndrome. J Electromyogr Kinesiol 2007; 19:22-9. [PMID: 17709261 DOI: 10.1016/j.jelekin.2007.06.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2007] [Revised: 06/29/2007] [Accepted: 06/29/2007] [Indexed: 11/21/2022] Open
Abstract
Motor unit properties were analyzed in patients with upper motor neuron syndrome (UMNS). Multi-channel surface electromyographic (EMG) signals were recorded for 300s from the biceps brachii muscle of seven male subacute patients (time from lesion, mean+/-SE, 4.9+/-1.0 months). In three patients, both arms were investigated, leading to 10 recorded muscles. Patients were analyzed in rest-like condition with motor units activated due to pathological muscle overactivity. For a total of 12 motor units, the complete discharge pattern was extracted from EMG decomposition. Interpulse interval variability was 7.8+/-0.9%. At minimum discharge rate (6.4+/-0.4 pulses per second, pps), conduction velocity was smaller than at maximum discharge rate (12.0+/-0.9pps) in all motor units (3.60+/-0.21m/s vs. 3.84+/-0.20m/s). Conduction velocity changed by 1.35+/-0.48% (different from zero, P<0.01) for each increase of 1pps in discharge rate. It was concluded that conduction velocity of low-threshold motor units in subacute patients with UMNS had similar values as reported in healthy subjects and was positively correlated to instantaneous discharge rate (velocity recovery function of muscle fibers).
Collapse
Affiliation(s)
- Isabella Campanini
- LAM Laboratorio Analisi Movimento (Dip. Riabilitazione) AUSL di Reggio Emilia, Correggio, Italy
| | | | | |
Collapse
|
54
|
Dibble LE, Hale TF, Marcus RL, Droge J, Gerber JP, LaStayo PC. High-intensity resistance training amplifies muscle hypertrophy and functional gains in persons with Parkinson's disease. Mov Disord 2007; 21:1444-52. [PMID: 16773643 DOI: 10.1002/mds.20997] [Citation(s) in RCA: 187] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Strength deficits in persons with Parkinson's disease (PD) have been identified as a contributor to bradykinesia. However, there is little research that examines the effect of resistance training on muscle size, muscle force production, and mobility in persons with PD. The purpose of this exploratory study was to examine, in persons with PD, the changes in quadriceps muscle volume, muscle force production, and mobility as a result of a 12-week high-force eccentric resistance training program and to compare the effects to a standard-care control. Nineteen individuals with idiopathic PD were recruited and consented to participate. Matched assignment for age and disease severity resulted in 10 participants in the eccentric group and 9 participants in the control group. All participants were tested prior to and following a 12-week intervention period with testing and training conducted at standardized times in their medication cycle. The eccentric group performed high-force quadriceps contractions on an eccentric ergometer 3 days a week for 12 weeks. The standard-care group exercise program encompassed standard exercise management of PD. The outcome variables were quadriceps muscle volume, muscle force, and mobility measures (6-minute walk, stair ascent/descent time). Each outcome variable was tested using separate one-way analyses of covariance on the difference scores. Muscle volume, muscle force, and functional status improvements occurred in persons with PD as a result of high-force eccentric resistance training. The eccentric group demonstrated significantly greater difference scores for muscle structure, stair descent, and 6-minute walk (P < 0.05). Magnitude of effect size estimators for the eccentric group consistently exceeded those in the standard-care group for all variables. To our knowledge, this is the first clinical trial to investigate and demonstrate the effects of eccentric resistance training on muscle hypertrophy, strength, and mobility in persons with PD. Additional research is needed to determine the anatomical and neurological mechanisms of the observed strength gains and mobility improvements.
Collapse
Affiliation(s)
- Leland E Dibble
- Division of Physical Therapy, University of Utah, Salt Lake City, Utah, USA.
| | | | | | | | | | | |
Collapse
|
55
|
Wagner JM, Dromerick AW, Sahrmann SA, Lang CE. Upper extremity muscle activation during recovery of reaching in subjects with post-stroke hemiparesis. Clin Neurophysiol 2006; 118:164-76. [PMID: 17097340 PMCID: PMC1868433 DOI: 10.1016/j.clinph.2006.09.022] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2006] [Revised: 09/21/2006] [Accepted: 09/27/2006] [Indexed: 11/25/2022]
Abstract
OBJECTIVE To investigate upper extremity muscle activation and recovery during the first few months after stroke. METHODS Subjects with hemiparesis following stroke were studied performing a reaching task at an acute time point (mean=9 days post-stroke) and then again at a subacute time point (mean=109 days post-stroke). We recorded kinematics and electromyographic activity of six upper extremity muscles. RESULTS At the acute time point, the hemiparetic group had delayed muscle onsets, lower modulation ratios, and higher relative levels of muscle activation (%MVIC) during reaching than controls. From the acute to the subacute time points, improvements were noted in all three variables. By the subacute phase, muscle onsets were similar to controls, while modulation ratios remained lower than controls and %MVIC showed a trend toward being greater in the hemiparetic group. Changes in muscle activation were differentially related to changes in reaching performance. CONCLUSIONS Our data show that improvements in muscle timing and decreases in the relative level of volitional activation may underlie improved reaching performance in the early months after stroke. SIGNIFICANCE Given that stroke is one of the leading causes of persistent physical disability, it is important to understand how the ability to activate muscles changes during the early phases of recovery after injury.
Collapse
Affiliation(s)
- Joanne M. Wagner
- Program in Physical Therapy, Washington University School of Medicine, St. Louis MO
| | - Alexander W. Dromerick
- Program in Physical Therapy, Washington University School of Medicine, St. Louis MO
- Department of Neurology, Washington University School of Medicine, St. Louis MO
- Program in Occupational Therapy, Washington University School of Medicine, St. Louis MO
- National Rehabilitation Hospital, Washington DC
| | - Shirley A. Sahrmann
- Program in Physical Therapy, Washington University School of Medicine, St. Louis MO
- Department of Neurology, Washington University School of Medicine, St. Louis MO
| | - Catherine E. Lang
- Program in Physical Therapy, Washington University School of Medicine, St. Louis MO
- Department of Neurology, Washington University School of Medicine, St. Louis MO
- Program in Occupational Therapy, Washington University School of Medicine, St. Louis MO
| |
Collapse
|
56
|
Pang MYC, Eng JJ. Muscle strength is a determinant of bone mineral content in the hemiparetic upper extremity: implications for stroke rehabilitation. Bone 2005; 37:103-11. [PMID: 15869927 PMCID: PMC3167823 DOI: 10.1016/j.bone.2005.03.009] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/29/2004] [Revised: 03/07/2005] [Accepted: 03/11/2005] [Indexed: 11/29/2022]
Abstract
Individuals with stroke have a high incidence of bone fractures and approximately 30% of these fractures occur in the upper extremity. The high risk of falls and the decline in bone and muscle health make the chronic stroke population particularly prone to upper extremity fractures. This was the first study to investigate the bone mineral content (BMC), bone mineral density (BMD), and soft tissue composition of the upper extremities and their relationship to stroke-related impairments in ambulatory individuals with chronic stroke (onset >1 year). Dual-energy X-ray absorptiometry (DXA) was used to acquire total body scans on 56 (22 women) community-dwelling individuals (>or=50 years of age) with chronic stroke. BMC (g) and BMD (g/cm2), lean mass (g), and fat mass (g) for each arm were derived from the total body scans. The paretic upper extremity was evaluated for muscle strength (hand-held dynamometry), impairment of motor function (Fugl-Meyer motor assessment), spasticity (Modified Ashworth Scale), and amount of use of the paretic arm in daily activities (Motor Activity Log). Results showed that the paretic arm had significantly lower BMC (13.8%, P<0.001), BMD (4.5%, P<0.001), and lean mass (9.0%, P<0.001) but higher fat mass (6.3%, P=0.028) than the non-paretic arm. Multiple regression analysis showed that lean mass in the paretic arm, height, and muscle strength were significant predictors (R2=0.810, P<0.001) of the paretic arm BMC. Height, muscle strength, and gender were significant predictors (R2=0.822, P<0.001) of lean mass in the paretic arm. These results highlight the potential of muscle strengthening to promote bone health of the paretic arm in individuals with chronic stroke.
Collapse
Affiliation(s)
- Marco YC Pang
- Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada
- Rehabilitation Research Laboratory, GF Strong Centre, Vancouver, British Columbia, Canada
| | - Janice J Eng
- Department of Physical Therapy, University of British Columbia, Vancouver, British Columbia, Canada
- Rehabilitation Research Laboratory, GF Strong Centre, Vancouver, British Columbia, Canada
| |
Collapse
|
57
|
Abstract
Spastic paresis follows chronic disruption of the central execution of volitional command. Motor function in patients with spastic paresis is subjected over time to three fundamental insults, of which the last two are avoidable: (1) the neural insult itself, which causes paresis, i.e., reduced voluntary motor unit recruitment; (2) the relative immobilization of the paretic body part, commonly imposed by the current care environment, which causes adaptive shortening of the muscles left in a shortened position and joint contracture; and (3) the chronic disuse of the paretic body part, which is typically self-imposed in most patients. Chronic disuse causes plastic rearrangements in the higher centers that further reduce the ability to voluntarily recruit motor units, i.e., that aggravate baseline paresis. Part I of this review focuses on the pathophysiology of the first two factors causing motor impairment in spastic paresis: the vicious cycle of paresis-disuse-paresis and the contracture in soft tissues.
Collapse
Affiliation(s)
- Jean-Michel Gracies
- Department of Neurology, Mount Sinai Medical Center, One Gustave L Levy Place, Annenberg 2/Box 1052, New York, New York 10029-6574, USA.
| |
Collapse
|
58
|
De Deyne PG, Hafer-Macko CE, Ivey FM, Ryan AS, Macko RF. Muscle molecular phenotype after stroke is associated with gait speed. Muscle Nerve 2004; 30:209-15. [PMID: 15266637 DOI: 10.1002/mus.20085] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The disability of patients after stroke is generally attributed to upper motor neuron defects, but secondary changes in paretic muscle may enhance the disability. We analyzed the molecular phenotype and metabolic profile of the paretic and nonparetic vastus lateralis (VL) and we measured the severity of gait deficit in 13 patients at least 6 months after ischemic stroke. The results showed a significant increase in the proportion of fast myosin heavy chain (MHC, 68 +/- 14%) in the paretic compared to the nonparetic VL (50 +/- 13%). The specific activity of citrate synthase and glyceraldehyde phosphodehydrogenase was not significantly different between the two sides. The proportion of fast MHC was inversely associated with severity of gait deficit indexed by self-selected walking speed in the paretic leg, but not the nonparetic leg. Our findings demonstrate significant and potentially modifiable secondary biologic changes in hemiparetic muscle phenotype that may contribute to the disability of stroke.
Collapse
Affiliation(s)
- Patrick G De Deyne
- Departments of Physical Therapy and Rehabilitation Science, University of Maryland School of Medicine, Baltimore, Maryland, USA.
| | | | | | | | | |
Collapse
|
59
|
Abstract
PURPOSE: This paper reviews the mechanisms underlying the inability to generate force in individuals with stroke and summarizes the effects of strength training in these individuals. In addition, a systematic review of studies that have incorporated progressive strengthening interventions in individuals with stroke is presented. SUMMARY OF KEY POINTS: Central (e.g., motor recruitment) and peripheral (e.g., muscle atrophy) sources may alter muscle strength in individuals with stroke and further investigations are needed to partition and quantify their effects. As to the effect of strength training interventions in individuals with stroke, the majority of studies (albeit with small samples) that evaluated muscle strength as an outcome demonstrated improvements. With regard to the effect of strength training on functional outcomes in individuals with stroke, positive outcomes were found in less rigorous pre-test/post-test studies, but more conflicting results with controlled trials. CONCLUSIONS: Although there is some suggestion that strength training alone can improve muscle strength, further research is required to optimize strength training and the transfer of these strength gains to functional tasks in individuals with stroke.
Collapse
|
60
|
Chapter 8 Effects of aging on motor unit structure and function. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s1567-4231(09)70118-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
|
61
|
Abstract
The aging-related motor handicap and the growing population of elderly citizens have enormous socioeconomic effects on the modern healthcare system. The mechanisms underlying impaired motor performance in old age are complex and involve the central and peripheral nervous systems and the muscle tissue itself. It is widely accepted that the aging-related loss of muscle mass, strength and quality has a significant detrimental impact on motor performance in old age and on the ability to recover from falls, resulting in an increased risk of fractures and dependency. Therefore, the prevention of falls and gait instability is a very important safety issue, and different intervention strategies have been used to improve motor performance among the aging population. There is general consensus that physical exercise is a powerful intervention to obtain long term benefits on muscle function, reduce the frequency of falls, and to maintain independence and a high quality of life in older persons. The results from studies using different types of hormone supplementation therapies have shown interesting and encouraging effects on skeletal muscle mass and function. However, the potential risks with both growth hormone and androgen treatment are not known and long term clinical trials are needed to address safety concerns and the effects on skeletal muscle. Recent advancements in cellular/molecular, physiological and molecular biological techniques will significantly facilitate our understanding of aging-related impairments of muscle function and contribute to the evaluation of different intervention strategies.
Collapse
Affiliation(s)
- L Larsson
- Noll Physiological Research Center, Pennsylvania State University, University Park 16802/6900, USA.
| | | |
Collapse
|
62
|
Sun TY, Chen JJ, Lin TS. Analysis of motor unit firing patterns in patients with central or peripheral lesions using singular-value decomposition. Muscle Nerve 2000; 23:1057-68. [PMID: 10883000 DOI: 10.1002/1097-4598(200007)23:7<1057::aid-mus8>3.0.co;2-a] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
We applied the singular value decomposition (SVD) method to study single motor unit firing patterns. Two projects were carried out: (1) a computer simulation study to confirm the meanings of two SVD parameters, the eigenvalue corresponding to the positive-slope eigenvector (PEV) and that corresponding to the negative-slope eigenvector (NEV); and (2) a clinical study for which electromyographic (EMG) recordings were made from first dorsal interosseous muscle in patients with stroke, myopathies, or neuropathies and in healthy control subjects. Results of computer simulation reveal that the NEV reflects the amount of instantaneous firing variability, whereas the PEV/NEV (P/N) ratio exhibits the relative effect of a trend in the firing pattern. In human studies, the P/N ratio of stroke patients was significantly higher than that of the controls, whereas their NEV was comparable. By contrast, in the myopathy and neuropathy groups, the NEV increased significantly, whereas the P/N ratio did not. These results suggest that the SVD method decomposes the motor unit (MU) firing variation into two components and that the mechanism for increased firing variability is different for supraspinal and spinal-infraspinal lesions.
Collapse
Affiliation(s)
- T Y Sun
- Institute of Biomedical Engineering, National Cheng-Kung University, Tainan, Taiwan
| | | | | |
Collapse
|
63
|
Abstract
Muscle fiber contractile dysfunction in myotonic dystrophy (MD) is poorly understood. We biopsied the tibialis anterior of two symptomatic and three asymptomatic subjects (aged 21-31 years) with the MD mutation. Biopsies were freeze dried. A total of 103 single muscle fibers were activated with Ca(++), allowing maximal force measurements and specific force (SF) estimates. The slack test was performed to calculate maximum unloaded shortening velocity (V(o)). The myosin heavy chain composition of each fiber was determined using sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). Type I and IIA fibers of all subjects had reduced SF when compared with healthy control subjects (P < 0.001). In addition, the type I fibers of symptomatic subjects generated less SF than those of asymptomatic subjects (P < 0.001). Type I fibers from asymptomatic and symptomatic subjects did not differ in V(o), but V(o) was lower than in control subjects (P < 0.001). There was no significant difference in V(o) of type IIA fibers from symptomatic, asymptomatic, and control subjects. These results indicate that the MD mutation leads to a diminished force-generating capacity of the myofilaments in both symptomatic and asymptomatic individuals. The results further suggest that reduction in force-generating capacity at the cellular level develops prior to clinical weakness.
Collapse
Affiliation(s)
- L S Krivickas
- Department of Physical Medicine and Rehabilitation, Spaulding Rehabilitation Hospital and Harvard Medical School, 125 Nashua St., Boston, Massachusetts 02114, USA.
| | | | | | | |
Collapse
|
64
|
Smith GV, Silver KH, Goldberg AP, Macko RF. "Task-oriented" exercise improves hamstring strength and spastic reflexes in chronic stroke patients. Stroke 1999; 30:2112-8. [PMID: 10512915 DOI: 10.1161/01.str.30.10.2112] [Citation(s) in RCA: 103] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND AND PURPOSE Despite the belief that after cerebral infarction only limited functional gains are possible beyond the subacute period, we tested the hypothesis that a 12-week program of "task-oriented" treadmill exercise would increase muscle strength and decrease spastic reflexes in chronic hemiparetic patients. METHODS Fourteen subjects, aged 66+/-3 (mean+/-SEM) years, with residual gait deviations due to remote stroke (>6 months), underwent repeated measures of reflexive and volitional (concentric and eccentric) torque with use of isokinetic dynamometry on the hamstring musculature bilaterally. Torque output was measured at 4 angular velocities (30(o), 60(o), 90(o), and 120(o)/s). RESULTS After 3 months of 3 times/wk low-intensity aerobic exercise, there were significant main effects (2 legs [P<0.01]x2 times [P<0. 01]x4 angular velocities [P<0.05]) for concentric torque production. Torque/time production in the concentric mode also improved significantly in the paretic (50%, P<0.01) and nonparetic hamstrings (31%, P<0.01). Eccentric torque/time production increased by 21% (P<0.01) and 22% (P<0.01) in the paretic and nonparetic hamstrings, respectively. Passive (reflexive) torque/time generation in the paretic hamstrings decreased by 11% (P<0.027). Reflexive torque/time was unchanged in the nonparetic hamstrings (P=0.45). CONCLUSIONS These findings provide evidence that progressive treadmill aerobic exercise training improves volitional torque and torque/time generation and reduces reflexive torque/time production in the hemiparetic limb. Strength changes associated with improved functional mobility in chronic hemiparetic stroke survivors after treadmill training will be reported in future articles.
Collapse
Affiliation(s)
- G V Smith
- Department of Physical Therapy, Division of Gerontology, University of Maryland-Baltimore School of Medicine, Baltimore, MD, USA.
| | | | | | | |
Collapse
|
65
|
Connelly DM, Rice CL, Roos MR, Vandervoort AA. Motor unit firing rates and contractile properties in tibialis anterior of young and old men. J Appl Physiol (1985) 1999; 87:843-52. [PMID: 10444648 DOI: 10.1152/jappl.1999.87.2.843] [Citation(s) in RCA: 232] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The effects of aging on motoneuron firing rates and muscle contractile properties were studied in tibialis anterior muscle by comparing results from six young (20.8 +/- 0.8 yr) and six old men (82.0 +/- 1.7 yr). For each subject, data were collected from repeated tests over a 2-wk period. Contractile tests included maximal voluntary contraction (MVC) with twitch interpolation and stimulated twitch contractions. The old men had 26% lower MVC torque (P < 0.01) than did the young men, but percent activation was not different (99.1 and 99.3%, respectively). Twitch contraction durations were 23% longer (P < 0.01) in the old compared with the young men. During a series of repeated brief steady-state contractions at 10, 25, 50, 75, and 100% MVC, motor unit firing rates were recorded. Results from approximately 950 motor unit trains in each subject group indicated that at all relative torque levels mean firing rates were 30-35% lower (P < 0.01) in the old subjects. Comparisons between young and old subjects' mean firing rates at each of 10%, 50%, and MVC torques and their corresponding mean twitch contraction duration yielded a range of moderate-to-high correlations (r = -0.67 to -0.84). That lower firing rates were matched to longer twitch contraction durations in the muscle of old men, and relatively higher firing rates were matched with shorter contraction times from the young men, indirectly supports the neuromuscular age-related remodeling principle.
Collapse
Affiliation(s)
- D M Connelly
- Center for Activity and Ageing, School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, Ontario, Canada N6A 3K7
| | | | | | | |
Collapse
|