A minimalistic model of resistance training : effects on skeletal muscle function during unloading

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Authors
Schulze, Kimberley E.
Advisor
Trappe, Scott William
Issue Date
1999
Keyword
Degree
Thesis (Ph. D.)
Department
School of Physical Education
Other Identifiers
Abstract

Since astronaut time and energy are at a premium, effective countermeasures must be designed to maximize benefits while minimizing time/energy cost. Therefore, our intent was to design and evaluate a low volume, high intensity resistance training program (RTP) on the preservation of knee extensor and plantar flexor size, strength and neuromuscular function in response to unloading. A total of 32 subjects participated. Sixteen men underwent 21 days of unilateral lower limb suspension (ULLS) and were assigned to control (no RTP) (ULLS-CON, n=8) or countermeasures (ULLS-CM, n=8). The remaining subjects were ambulatory for 21 days and were assigned to no RTP (n=8) or countermeasures (n=8). Countermeasure subjects performed RTP every third day during the suspension period (total=6). The RTP consisted of 2 maximal isometric contractions (MVC), 1 set of 10 concentric/eccentric isotonic repetitions, and 1 set to exhaustion, at 80% of 1-repetition maximum (1RM). There was no change in muscle function in ambulatory subjects. Whole muscle cross sectional area (CSA) measured by computed tomography (CT) decreased 7% (thigh) and 7.5% (calf) in ULLS-CON (p<0.05), and was unchanged in ULLS-CM. MVC decreased 16.5% in both quadricep and calf muscles in ULLS-CON (p<0.05) and increased 6% in the quadricep of ULLSCM (p<0.05). Maximal concentric (CNC) and eccentric (ECC) isokinetic strength decreased an average of 18% and 17% in the knee extensors and plantar flexors of ULLS-CON, respectively (p<0.05) and was unchanged in ULLS-CM. 1RM decreased 16% in both quadricep and calf of ULLS-CON (p<0.05) and was unchanged in ULLSCM. Knee extensor work capacity, evaluated during 30 maximal CNC contractions (3.14 rad•sec-'), decreased 18% in ULLS-CON (p<0.05). Neural activation of knee extensors and plantar flexors was measured by electromyography (EMG). Submaximal v.lat, v.med, gast and sol EMG increased in ULLS-CON (p<0.05) and was unaltered in ULLSCM. Maximal EMG decreased 20% and 26% in v.1at and v.med, respectively in ULLSCON (p<0.05). ULLS-CM showed a 15% and 28% increase in v.med and gast maximal EMG (p<0.05). These data suggest knee extensor and plantar flexor muscle size, strength and neuromuscular function were preserved during unloading using a low volume, high intensity RTP performed every third day.