KITAHARA, A., T. HAMAOKA, N. MURASE, T. HOMMA, Y. KUROSAWA, C. UEDA, T. NAGASAWA, S. ICHIMURA, M. MOTOBE, K. YASHIRO, S. NAKANO, and T. KATSUMURA. Deterioration of Muscle Function after 21-Day Forearm Immobilization. Med. Sci. Sports Exerc., Vol. 35, No. 10, pp. 1697–1702, 2003.
Purpose: Although it is well known that immobilization causes muscle atrophy, most immobilization models have examined lower limbs, and little is known about the forearm. The purpose of this study was to determine whether forearm immobilization produces changes in muscle morphology and function.
Methods: Six healthy males (age: 21.5 ± 1.4, mean ± SD) participated in this study. The nondominant arm was immobilized with a cast (CAST) for 21 d, and the dominant arm was measured as the control (CONT). The forearm cross-sectional area (CSA) and circumference were measured as muscle morphology. Maximum grip strength, forearm muscle oxidative capacity, and dynamic grip endurance were measured as muscle function. Magnetic resonance (MR) imaging was used to measure CSA, and 31phosphorus MR spectroscopy was used to measure time constant (Tc) for phosphocreatine (PCr) recovery after submaximal exercise (PCr-Tc). Grip endurance was expressed by the number of handgrip contractions at 30% maximum grip strength load. All measurements were taken before and after the immobilization.
Results: After the 21-d forearm immobilization, no changes were seen for each measurement in CONT. CSA and the circumference showed no significant changes in CAST. However, maximum grip strength decreased by 18% (P < 0.05), PCr-Tc was prolonged by 45% (P < 0.05), and the grip endurance at the absolute load was reduced by 19% (P < 0.05) for CAST.
Conclusion: In this model, 21-d forearm immobilization caused no significant changes in forearm muscle morphology, but the muscle function showed remarkable deterioration ranging from 18 to 45%.
Human muscle atrophy results from muscle disuse, for example, bed rest (1,4,7–9,24), the unloading of a limb by suspension (6,13), or the microgravity environment during a space flight (10,17,24). Most recent studies examining changes in lower limbs have noted remarkable deterioration in both muscle morphology and function from muscle disuse (1,2,4,6–10,13,17,24). Furthermore, many studies have been done to establish effective countermeasures for the space flight environment (4,10). However, the lower-limb muscles are mostly weight bearing, and therefore the positioning and volume of these muscles are different from those in the forearm. Lower-limb muscles are likely more affected by the microgravity environment than those of the forearm. Although the forearm may be involved in many important activities in a microgravity environment, few studies have determined the extent of forearm muscle atrophy by disuse (18,19,23). Therefore, it seems very important to evaluate muscle structural and functional changes in the forearm, and also to verify effective countermeasures to prevent those changes. It has been reported that 2 wk of microgravity environment is long enough to produce muscle atrophy in the lower limbs (2), although the reduction rate of the cross-sectional area (CSA), muscle volume, maximum muscle strength, and the fatigabilities are not always parallel (1,2,4,6–10,13,17–19,23,24). The forearm may go through a different process of atrophy compared with lower limbs. To investigate this process we selected a 21-d forearm immobilization model, a period long enough to produce muscle changes in the lower limbs.
Muscle strength, torque, and fatigability as indicators of muscle function have been measured in many studies (2,4,6,7,10,13,17–19,23,24). However, only a few studies have measured the changes of muscle oxidative capacity by the use of biopsy specimens (7,9,10,18,19,24).
We estimated muscle oxidative capacity using 31phosphorous magnetic resonance spectroscopy (31P-MRS), as well as grip strength and grip endurance as indications of muscle function. As for the muscle morphology, we measured the forearm CSA and circumference. Therefore, the purpose of this study was to examine whether 21-d forearm immobilization produces changes in muscle morphology and function.