Resistance and functional training reduces knee extensor position fluctuations in functionally limited older adults

Abstract

The purpose of this study was to determine the effect of task-specificity on knee extensor steadiness adaptations in functionally limited older adults. Twenty-four functionally limited older adults (74.6+/-7.6 years: 22 women, 2 men) completed a 10-week control period followed by 10 weeks (2 days/week) of resistance (RT), functional (FT) (practicing everyday tasks, i.e., chair rises) or functional + resistance (FRT) training, which featured both shortening and lengthening movements. During testing, subjects performed a steady isometric [10, 25, 50% of maximal voluntary contraction (MVC)] and shortening/lengthening (5, 30, 65% of MVC) knee extensor contractions. There were no steadiness (isometric, shortening or lengthening contractions) changes in the control period and no adaptations in isometric steadiness due to training. RT induced a 37% reduction in shortening fluctuations at 5% of MVC and 35% reduction in lengthening fluctuations at both 30% and 65% of MVC. FRT induced a 60% reduction in shortening fluctuations at 30% of MVC. No adaptations in dynamic steadiness were observed in the FT group. Further analysis indicated that those who were the least steady at baseline showed the greatest training effects during isometric (RT: R (2)=0.25, FRT: R (2)=0.49, FT: R (2)=0.38), shortening (RT: R (2)=0.36, FRT: R (2)=0.36, FT: R (2)=0.35) and lengthening (RT: r (2)=0.29, FRT: r (2)=0.44) contractions. In conclusion, steadiness improvements in groups performing resistance exercise, without a concomitant improvement in the FT group, supports a role for task-specificity in explaining steadiness adaptations, particularly for unsteady older adults.

Low-frequency Force Steadiness Practice in Plantar Flexor Muscle Reduces Postural Sway during Quiet Standing

“…Thus, the practice effect on postural stability was dependent on the prepractice postural stability. This relationship is also consistent with other reports documenting that improvements in steadiness are more likely in subjects with low initial steadiness levels (Manini et al, 2005;Tracy et al, 2004), and therefore, strengthens the notion that the effectiveness of the training is dependent on the initial level of steadiness.…”

Functional Significance of Force Fluctuation During Voluntary Muscle Contraction

“…Thus, the effects of practice on postural stability are dependent on prepractice postural stability. This finding is also consistent with the findings of other reports demonstrating that improvements in steadiness are more frequent in subjects with low initial steadiness levels (Manini et al, 2005;Tracy et al, 2004); this strengthens the notion that the effectiveness of training is dependent on the initial level of steadiness. (Oshita and Yano, 2011c) As indicated in section 4, multiple factors influence the relationship between force steadiness and postural stability.…”

Effect of mental fatigue on induced tremor in human knee extensors

“…Previous studies have shown that induced tremor increases as the level of muscle activity increases [Joyce and Rack, 1974;Manini et al, 2005;Matthews and Muir, 1980]. Thus the observed reduction in tremor cannot be related to the reduction in MVC.…”