Leg fidgeting alleviates reduced oxygen extraction in the gastrocnemius muscle caused by prolonged sitting: a randomized crossover trial.

Purpose: Oxygen extraction in skeletal muscle is an important determinant of exercise tolerance. Prolonged sitting decreases oxygen extraction in the gastrocnemius muscle. However, the underlying mechanism remains unknown, and preventive measures are yet to be established. Therefore, we aimed to elucidate the mechanism by which prolonged sitting decreased muscle oxygen extraction and investigate preventive measures.

Methods: Ten healthy young males (age 21.2 ± 0.4 years; body mass index, 20.5 ± 1.3 kg/m) were randomly assigned to each of the following conditions: 3-h supine (CON), 3-h sitting (SIT), and 3-h fidgeting of one lower leg during sitting (FID). Oxygen extraction from the gastrocnemius muscle was measured using near-infrared spectroscopy and the vascular occlusion test under each condition. The rate of change in total Hb + Mb (THb) was measured as an indicator of venous stasis and interstitial fluid accumulation in the lower leg.

Results: Muscle oxygen extraction was significantly lower at 180 min for SIT and FID than for CON (4384.2 ± 1426.8; 5281.5 ± 1823.7; 6517.4 ± 1390.8 a.u., respectively) and significantly higher for FID than for SIT (5281.5 ± 1823.7 vs. 4384.2 ± 1426.8 a.u., respectively). The rate of THb change was significantly higher at 180 min for SIT than for CON and FID (12.9 ± 15.1; -2.3 ± 5.7; 2.2 ± 11.6%, respectively). However, no significant difference was observed between CON and FID.

Conclusion: We found that 3-h prolonged sitting reduced oxygen extraction in the gastrocnemius muscles due to reduced oxygen supply to capillaries and increased distance between capillaries and myocytes. However, leg fidgeting alleviated this effect in healthy young males.

Trial Registration Number: UMIN000050531 (March 8, 2023).