Endpoint accuracy for a small and a large hand muscle in young and old adults during rapid, goal-directed isometric contractions

2008 ◽  
Vol 187 (3) ◽  
pp. 373-385 ◽  
Author(s):  
Brach Poston ◽  
Joel A. Enoka ◽  
Roger M. Enoka
Keyword(s):  
Isometric Contractions ◽  
Old Adults ◽  
Hand Muscle

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

2003 ◽  
Vol 94 (3) ◽  
pp. 966-974 ◽  
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.

Older adults are less steady during submaximal isometric contractions with the knee extensor muscles

2002 ◽  
Vol 92 (3) ◽  
pp. 1004-1012 ◽  
Author(s):  
Brian L. Tracy ◽  
Roger M. Enoka
Keyword(s):  
Maximum Voluntary Contraction ◽  
Knee Extensor ◽  
Voluntary Contraction ◽  
Eccentric Contractions ◽  
Isometric Contractions ◽  
Antagonist Muscle ◽  
Old Adults ◽  
Extensor Muscles ◽  
Young Subjects ◽  
Knee Extensor Muscles

This study compared the steadiness of submaximal contractions with the knee extensor muscles in young and old adults. Twenty young and twenty old subjects underwent assessment of isometric maximum voluntary contraction (MVC), one-repetition maximum (1-RM) strength, and steadiness during isometric, concentric, and eccentric contractions with the knee extensor muscles. The old adults displayed 33% lower MVC force and a 41% lower 1-RM load. The coefficient of variation for force was significantly greater for the old adults during isometric contractions at 2, 5, and 10% of MVC but not at 50% MVC. The decline in steadiness at low forces experienced by the men was marginally greater than that experienced by the women. The steadiness of concentric and eccentric contractions was similar in young and old adults at 5, 10, and 50% of 1-RM load. Old subjects exhibited greater coactivation of an antagonist muscle compared with young subjects during the submaximal isometric and anisometric contractions. These results indicate that, whereas the ability to exert steady submaximal forces with the knee extensor muscles was reduced in old adults, fluctuations in knee joint angle during slow movements were similar for young and old adults.

The Relationships Between Muscle Force Steadiness and Visual Steadiness in Young and Old Adults

Motor Control ◽  
2015 ◽  
Vol 19 (1) ◽  
pp. 60-74 ◽  
Author(s):  
Rebecca L. Krupenevich ◽  
Nick Murray ◽  
Patrick M. Rider ◽  
Zachary J. Domire ◽  
Paul DeVita
Keyword(s):  
Eye Movements ◽  
Force Control ◽  
Muscle Force ◽  
Age Groups ◽  
Quadriceps Muscle ◽  
Voluntary Contraction ◽  
Isometric Contractions ◽  
Old Adults ◽  
Visual Ability ◽  
Muscle Torque

Since vision is used in studies of muscle force control, reduced muscle force control might be related to reduced visual ability. We investigated relationships between steadiness in eye movements and quadriceps muscle torque (a surrogate for force) during isometric contractions of constant and varying torques. Nineteen young adults with an average age of 20.7 years and 18 old adults with an average age of 71.6 years performed three vision tasks, three vision and torque tasks at 40% maximal voluntary contraction (MVC), and three vision and torque tasks at 54 nm. Age groups had identical torque steadiness (CV) in 40%-MVC and 54-nm conditions (p > .05). Old had similar vertical (p > .05) but decreased horizontal visual steadiness (SD) (p < .05) compared with young. Correlations between visual steadiness and muscle torque steadiness failed to show a significant relationship (p > .05). We were unable to identify a substantial relationship between muscle torque steadiness and eye movement, as a component of visual steadiness, and conclude that reduced visual steadiness does not contribute to reduced muscle torque steadiness.

Strength training reduces force fluctuations during anisometric contractions of the quadriceps femoris muscles in old adults

2004 ◽  
Vol 96 (4) ◽  
pp. 1530-1540 ◽  
Author(s):  
Brian L. Tracy ◽  
William C. Byrnes ◽  
Roger M. Enoka
Keyword(s):  
Strength Training ◽  
Angular Displacement ◽  
Quadriceps Femoris ◽  
Voluntary Contraction ◽  
Isometric Contractions ◽  
Heavy Load ◽  
Old Adults ◽  
Training Groups ◽  
Force Fluctuations ◽  
Quadriceps Femoris Muscles

The greater fluctuations in motor output that are often exhibited by old adults can be reduced with strength training. The purpose of the study was to determine the effect of strength and steadiness training by old adults on fluctuations in force and position during voluntary contractions with the quadriceps femoris muscle. Healthy old adults (65-80 yr) completed 16 wk of heavy-load (80% of maximum, n = 11) strength training, heavy-load steadiness training ( n = 6), or no training ( n = 9). Steadiness training required subjects to match the angular displacement about the knee joint to a constant-velocity template. The Heavy-Load group experienced a 5.5% increase in muscle volume, a 25% increase in maximal voluntary contraction force, and a 26% increase in the one-repetition (1-RM) load. The Heavy-Load Steady group experienced increases of 11.5, 31, and 36%, respectively. The maximal electromyogram signal of quadriceps femoris increased by 51% in the two training groups. The coefficient of variation (CV) for force during submaximal isometric contractions did not change with training for any group. Although both training groups also experienced a reduction in CV for force during anisometric contractions with a 50% 1-RM load, the standard deviation of position did not change with time for any group. The Heavy-Load Steady group also experienced a reduction in CV for force during the training contractions performed with the 80% 1-RM load. Thus strength training reduced the force fluctuations of the quadriceps femoris muscles during anisometric contractions but not during isometric contractions.

Strength training improves the steadiness of slow lengthening contractions performed by old adults

1999 ◽  
Vol 87 (5) ◽  
pp. 1786-1795 ◽  
Author(s):  
Douglass H. Laidlaw ◽  
Kurt W. Kornatz ◽  
Douglas A. Keen ◽  
Shuji Suzuki ◽  
Roger M. Enoka
Keyword(s):  
Strength Training ◽  
Training Program ◽  
Muscle Activation ◽  
Voluntary Contraction ◽  
Heavy Load ◽  
Lengthening Contractions ◽  
Old Adults ◽  
Hand Muscle ◽  
Heavy Loads ◽  
Shortening Contractions

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.

scholarly journals Recruitment and derecruitment characteristics of motor units in a hand muscle of young and old adults

2010 ◽  
Vol 108 (6) ◽  
pp. 1659-1667 ◽  
Author(s):  
Mark Jesunathadas ◽  
Adam R. Marmon ◽  
James M. Gibb ◽  
Roger M. Enoka
Keyword(s):  
Motor Unit ◽  
Discharge Rate ◽  
Age Groups ◽  
Motor Units ◽  
Motor Unit Recruitment ◽  
Force Variability ◽  
Old Adults ◽  
Hand Muscle ◽  
The Difference ◽  
Ramp Contractions

The significant decline in motor neuron number after ∼60 yr of age is accompanied by a remodeling of the neuromuscular system so that average motor unit force increases and the ability of old adults to produce an intended force declines. One possible explanation for the loss of movement precision is that the remodeling increases the difference in recruitment forces between successively recruited motor units in old adults and this augments force variability at motor unit recruitment. The purpose of the study was to compare the forces and discharge characteristics of motor units in a hand muscle of young and old adults at motor unit recruitment and derecruitment. The difference in recruitment force between pairs of motor units did not differ between young ( n = 54) and old adults ( n = 56; P = 0.702). However, old adults had a greater proportion of contractions in which motor units discharged action potentials transiently before discharging continuously during the ramp increase in force (young: 0.32; old: 0.41; P = 0.045). Force variability at motor unit recruitment was greater for old adults compared with young adults ( P ≤ 0.010), but discharge rate and discharge variability did not differ between age groups ( P ≥ 0.729). These results suggest that the difference in force between the recruitment of successive motor units does not differ between age groups, but that motor unit recruitment may be more transient and could contribute to the greater variability in force observed in old adults during graded ramp contractions.

Rate of tension development in isometric contractions of a human hand muscle

1981 ◽  
Vol 73 (1) ◽  
pp. 267-285 ◽  
Author(s):  
Robert G. Miller ◽  
Alar Mirka ◽  
Melanie Maxfield
Keyword(s):  
Human Hand ◽  
Isometric Contractions ◽  
Tension Development ◽  
Hand Muscle
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