JoCarol E. Shields1, Rob J. MacLennan1, Claire M. Smith1, Shawn M. Reese1, Alex A. Olmos1, & Jason M. DeFreitas1

1Oklahoma State University, Stillwater, Oklahoma

Mechanical stress placed on the limb has long been thought to induce muscular adaptations. Recently, it has been suggested that training-induced increases in muscle size are not necessarily the cause of increases in strength. Supporting that controversial proposal, age-related muscle atrophy (sarcopenia) has shown poor relationships with age-related declines in strength (dynapenia). Further exploration of the potential causal relationship of muscle size and strength is warranted. PURPOSE: To further examine this relationship by directly inducing muscle atrophy from 2 weeks of lower-limb immobilization. We hypothesized a strong, positive relationship by which the subjects that exhibit the most atrophy are also the ones that show the greatest strength loss. METHODS: Ten subjects (19-29 yrs.) have volunteered for this ongoing study, but only 5 have completed the protocol in full. Cross-sectional area (CSA) of the tibialis anterior (TA) muscle via ultrasound imaging and maximal voluntary contractions (MVC) of the dorsiflexors were taken prior to and after 2 weeks of left-leg immobilization. Crutches were used during the 2 weeks for mobility. An exploratory one-tailed Pearson correlation (n = 5) was used to estimate the potential relationship for a larger, appropriately powered study. RESULTS: A moderate, but negative, relationship was shown between changes in CSA and strength (r = -.660) (shown in Figure). CONCLUSION: Our preliminary findings suggest that greater atrophy does not necessarily lead to greater losses in strength. This data, albeit exploratory, does not currently support a causal relationship between muscle size and strength, and the relationship shown was in the opposite direction than hypothesized. However, strength is a complicated measure affected by various other factors (neural factors, muscle architecture, etc.) that could also change with disuse. A multifactorial analysis that includes the many elements leading to strength is needed.

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Figure 1

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