Deterioration of muscle function after 21-day forearm immobilization.
OBJECTIVE
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.


CONCLUSIONS
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%.
Kitahara
Aya
A
Department of Preventive Medicine and Public Health, Tokyo Medical University, 6-1-1 Shinjuku, Shinjuku-ku, Tokyo 160-8402, Japan. Ayakitahar@aol.com
Hamaoka
Takafumi
T
Murase
Norio
N
Homma
Toshiyuki
T
Kurosawa
Yuko
Y
Ueda
Chihoko
C
Nagasawa
Takeshi
T
Ichimura
Shiro
S
Motobe
Mayuko
M
Yashiro
Kazuya
K
Nakano
Shouichi
S
Katsumura
Toshihito
T
D000328:Adult; D002370:Casts, Surgical; D005542:Forearm; D018737:Hand Strength; D006801:Humans; D007103:Immobilization; D008297:Male; D009132:Muscles / Q000503:physiopathology*; D009133:Muscular Atrophy; D010084:Oxidation-Reduction; D010807:Physical Endurance