Effects of Oral Contraceptives and Biological Sex on Grip Strength and Excitation during Immobilization and Recovery:...

Females often experience greater weakness following immobilization compared with males. Hormonal fluctuations from the menstrual cycle or oral contraceptive (OC) use may contribute to sex differences and response variation.

We examined changes in peak and rapid force and surface electromyographic excitation among females using monophasic OC and females not using OC following immobilization and rehabilitation. To examine potential sex differences, a male control group was included.

Ten males, 10 OC females, and 10 non-OC females (mean ± standard deviation age = 23 ± 3 yr) immobilized their left wrist/hand with a brace for 1 wk, followed by ≥1 wk of rehabilitation. Participants completed grip tests to assess peak force and the rate of force development before and after immobilization and postrehabilitation, with electromyographic signals recorded from the extensor carpi radialis brevis and flexor digitorum superficialis.

Grip force declined postimmobilization: males = -17.2 ± 10.3%, non-OC = -22.3 ± 24.7%, OC = -20.7 ± 14.8%. No significant time-group interactions were observed for any dependent variables ( P > 0.05, η² p ≤ 0.084). Time effects showed recovery postrehab across all groups. Rate of force development, particularly at 200 ms, declined posttest and rebounded postrehab. Extensor carpi radialis brevis excitation increased postrehab; flexor digitorum superficialis excitation responses were highly variable across participants. Five participants required >1 wk of rehabilitation (two males, two non-OC, and one OC), suggesting rapid recovery for most.

Males and females in this study exhibited similar declines and recovery in grip force after 1 wk of wrist/hand immobilization, regardless of OC use. These findings suggest that the influence of OC use on neuromuscular outcomes in females undergoing short-term musculoskeletal rehabilitation may be minimal.