Modulation of intracortical inhibition during shortening and lengthening contractions of a hand muscle in young and old adults

When old adults participate in a strength-training program with heavy loads, they experience an increase in muscle strength and an improvement in the steadiness of submaximal isometric contractions. The purpose of this study was to determine the effect of light- and heavy-load strength training on the ability of old adults to perform steady submaximal isometric and anisometric contractions. Thirty-two old adults (60–91 yr) participated in a 4-wk training program of a hand muscle. Both the light- and heavy-load groups increased one-repetition maximum and maximal voluntary contraction (MVC) strength and experienced similar improvements in the steadiness of the isometric and shortening and lengthening contractions. The increase in MVC strength was greater for the heavy-load group and could not be explained by changes in muscle activation. Before training, the lengthening contractions were less steady than the shortening contractions with the lightest loads (10% MVC). After training, there was no difference in steadiness between the shortening and lengthening contractions, except with the lightest load. These improvements were associated with a reduced level of muscle activation, especially during the lengthening contractions.

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Older Adults Use a Unique Strategy to Lift Inertial Loads With the Elbow Flexor Muscles

Journal of Neurophysiology ◽

10.1152/jn.2000.83.4.2030 ◽

2000 ◽

Vol 83 (4) ◽

pp. 2030-2039 ◽

Cited By ~ 83

Author(s):

Andrew E. Graves ◽

Kurt W. Kornatz ◽

Roger M. Enoka

Keyword(s):

Young Adults ◽

Elbow Joint ◽

Muscle Activation ◽

Angular Displacement ◽

Elbow Flexor ◽

Lengthening Contractions ◽

Old Adults ◽

Flexor Muscles ◽

Elbow Flexor Muscles ◽

Target Force

The purpose of this study was to determine the effect of age on the ability to exert steady forces and to perform steady flexion movements with the muscles that cross the elbow joint. An isometric task required subjects to exert a steady force to match a target force that was displayed on a monitor. An anisometric task required subjects to raise and lower inertial loads so that the angular displacement around the elbow joint matched a template displayed on a monitor. Steadiness was measured as the coefficient of variation of force and as the normalized standard deviation of wrist acceleration. For the isometric task, steadiness as a function of target force decreased similarly for old adults and young adults. For the anisometric task, steadiness increased as a function of the inertial load and there were significant differences caused by age. Old adults were less steady than young adults during both shortening and lengthening contractions with the lightest loads. Furthermore, old adults were least steady when performing lengthening contractions. These behaviors appear to be associated with the patterns of muscle activation. These results suggest that different neural strategies are used to control isometric and anisometric contractions performed with the elbow flexor muscles and that these strategies do not change in parallel with advancing age.

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Contralateral activity in a homologous hand muscle during voluntary contractions is greater in old adults

Journal of Applied Physiology ◽

10.1152/japplphysiol.00836.2002 ◽

2003 ◽

Vol 94 (3) ◽

pp. 966-974 ◽

Cited By ~ 46

Author(s):

Minoru Shinohara ◽

Kevin G. Keenan ◽

Roger M. Enoka

Keyword(s):

Rate Of Change ◽

Isometric Contractions ◽

Average Force ◽

Heavy Load ◽

Old Adults ◽

Target Force ◽

Hand Muscle ◽

Young Subjects ◽

Voluntary Contractions ◽

Contralateral Muscle

This study compared the amount of contralateral activity produced in a homologous muscle by young (18–32 yr) and old (66–80 yr) adults when they performed unilateral isometric and anisometric contractions with a hand muscle. The subjects were not aware that the focus of the study was the contralateral activity. The tasks involved the performance of brief isometric contractions to six target forces, slowly lifting and lowering six inertial loads, and completing a set of 10 repetitions with a heavy load. The unintended force exerted by the contralateral muscle during the isometric contractions increased with target force, but the average force was greater for the old adults (means ± SD; 12.6 ± 15.3%) compared with the young adults (6.91 ± 11.1%). The contralateral activity also increased with load during the anisometric contractions, and the average contralateral force was greater for the old subjects (5.28 ± 6.29%) compared with the young subjects (2.10 ± 3.19%). Furthermore, the average contralateral force for both groups of subjects was greater during the eccentric contractions (4.17 ± 5.24%) compared with the concentric contractions (3.20 ± 5.20%). The rate of change in contralateral activity during the fatigue task also differed between the two groups of subjects. The results indicate that old subjects have a reduced ability to suppress unintended contralateral activity during the performance of goal-directed, unilateral tasks.

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Shoulder position and lesion location differentially affect hand muscle excitability and intracortical inhibition early post-stroke

Brain Stimulation ◽

10.1016/j.brs.2021.10.331 ◽

2021 ◽

Vol 14 (6) ◽

pp. 1691-1692

Author(s):

Shashwati Geed ◽

Michelle Harris-Love ◽

Megan Grainger ◽

Harrish Ganesh ◽

Matthew Edwardson ◽

...

Keyword(s):

Intracortical Inhibition ◽

Lesion Location ◽

Post Stroke ◽

Hand Muscle ◽

Shoulder Position ◽

Muscle Excitability

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Motor unit synchronisation is enhanced during slow lengthening contractions of a hand muscle

The Journal of Physiology ◽

10.1113/jphysiol.2002.026948 ◽

2002 ◽

Vol 545 (2) ◽

pp. 681-695 ◽

Cited By ~ 93

Author(s):

John G. Semmler ◽

Kurt W. Kornatz ◽

Devin V. Dinenno ◽

Shi Zhou ◽

Roger M. Enoka

Keyword(s):

Motor Unit ◽

Lengthening Contractions ◽

Hand Muscle

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Corticomotor plasticity and learning of a ballistic thumb training task are diminished in older adults

Journal of Applied Physiology ◽

10.1152/japplphysiol.00443.2009 ◽

2009 ◽

Vol 107 (6) ◽

pp. 1874-1883 ◽

Cited By ~ 101

Author(s):

Nigel C. Rogasch ◽

Tamara J. Dartnall ◽

John Cirillo ◽

Michael A. Nordstrom ◽

John G. Semmler

Keyword(s):

Older Adults ◽

Primary Motor Cortex ◽

Motor Evoked Potentials ◽

Short Interval ◽

Intracortical Inhibition ◽

Training Task ◽

Abductor Pollicis Brevis ◽

Corticomotor Excitability ◽

Old Adults ◽

Young Subjects

This study examined changes in corticomotor excitability and plasticity after a thumb abduction training task in young and old adults. Electromyographic (EMG) recordings were obtained from right abductor pollicis brevis (APB, target muscle) and abductor digiti minimi (ADM, control muscle) in 14 young (18–24 yr) and 14 old (61–82 yr) adults. The training task consisted of 300 ballistic abductions of the right thumb to maximize peak thumb abduction acceleration (TAAcc). Transcranial magnetic stimulation (TMS) of the left primary motor cortex was used to assess changes in APB and ADM motor evoked potentials (MEPs) and short-interval intracortical inhibition (SICI) before, immediately after, and 30 min after training. No differences in corticomotor excitability (resting and active TMS thresholds, MEP input-output curves) or SICI were observed in young and old adults before training. Motor training resulted in improvements in peak TAAcc in young (177% improvement, P < 0.001) and old (124%, P = 0.005) subjects, with greater improvements in young subjects ( P = 0.002). Different thumb kinematics were observed during task performance, with increases in APB EMG related to improvements in peak TAAcc in young ( r2 = 0.46, P = 0.008) but not old ( r2 = 0.09, P = 0.3) adults. After training, APB MEPs were 50% larger ( P < 0.001 compared with before) in young subjects, with no change after training in old subjects ( P = 0.49), suggesting reduced use-dependent corticomotor plasticity with advancing age. These changes were specific to APB, because no training-related change in MEP amplitude was observed in ADM. No significant association was observed between change in APB MEP and improvement in TAAcc with training in individual young and old subjects. SICI remained unchanged after training in both groups, suggesting that it was not responsible for the diminished use-dependent corticomotor plasticity for this task in older adults.

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2326

Journal of Clinical and Translational Science ◽

10.1017/cts.2017.222 ◽

2017 ◽

Vol 1 (S1) ◽

pp. 62-62

Author(s):

Shashwati Geed ◽

Peter S. Lum ◽

Michelle L. Harris-Love ◽

Jessica Barth ◽

Peter E. Turkeltaub ◽

...

Keyword(s):

Muscle Activation ◽

Intracortical Inhibition ◽

Stroke Recovery ◽

Chronic Patients ◽

Corticomotor Excitability ◽

Hand Muscles ◽

Post Stroke ◽

Clinical Recovery ◽

Hand Muscle ◽

Hand Coordination

OBJECTIVES/SPECIFIC AIMS: Upper-extremity (UE) impairment affects 88% of stroke survivors due to dysfunctional shoulder-hand coordination. Patients may be able to grasp with the arm at rest, but unable to grasp in a functional context (eg, from a high shelf) because shoulder use elicits involuntary hand muscle activity. Further, much rehabilitation research is directed at unsuccessful stroke recovery (patients with persistent UE impairment) but very little towards patients who show successful clinical recovery (such as those with mild UE impairment) even though these patients have attained the desired rehabilitation outcome. We examined the neurophysiological trajectory of successful compared to unsuccessful post-stroke recovery in the context of functional UE movements to clearly identify what factors are necessary for successful recovery of functional UE movements after stroke. METHODS/STUDY POPULATION: We studied 3 populations: (1) mildly-impaired patients, early (at <17 d, 30 d, 90 d, and 180 d) after stroke as a model of successful post-stroke recovery, (2) moderately-impaired, chronic patients (>6-months post stroke) with persistent hand function impairment, as a model of incomplete post-stroke recovery (unsuccessful recovery), and (3) Healthy age-range matched controls. We used transcranial magnetic stimulation (TMS) in all 3 groups at the given time points to measure corticomotor excitability (motor evoked potentials, recruitment curve), corticomotor inhibition (short-interval intracortical inhibition, long-interval intracortical inhibition), and intracortical facilitation of hand muscles with the shoulder positioned in different degrees of flexion or abduction (these shoulder positions are known to elicit involuntary, undesired hand muscle activation, which leads to UE dysfunction and impairment in individuals with stroke). RESULTS/ANTICIPATED RESULTS: Data collection are in process and will be presented. Preliminary data from controls shows that corticomotor excitability of selected hand muscles is affected by changes in shoulder position. Preliminary findings in controls are consistent with clinical findings in stroke that certain shoulder positions elicit involuntary and undesired hand muscle activation, leading to UE dysfunction and disability. Findings from the stroke groups will be presented. DISCUSSION/SIGNIFICANCE OF IMPACT: We hypothesize that this centrally-facilitated coupling between shoulder and hand muscles is disrupted after stroke, which may play a central role in the inability of patients to perform functional UE movements. By comparing the TMS metrics in mildly-impaired Versus moderately-impaired chronic patients, we will be able to identify the longitudinal change in neurophysiology underlying shoulder-hand coordination that is associated with successful or unsuccessful clinical recovery of UE function after stroke. Thus, these findings will help us distinguish between the neurophysiology underlying successful from unsuccessful UE recovery leading to more mechanism-based interventions for UE dysfunction post stroke in the future.

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