Effect of small variations in hydration status due to 12-hour fasting on lower limb muscle function in middle-aged...

Evidence on the effects of low-grade dehydration on muscle function in non-athletic middle-aged adults is scarce and inconclusive. The objective was to assess the effect of small variations in hydration status due to 12-hour overnight fasting on right-leg muscle function in middle-aged adults.

Single-group before-and-after study in volunteers aged 35-65 years. Participants were assessed at two time points: after 12 hours of absolute fasting and after breakfast and drinking 1.5 L of water. Body composition and hydration status were assessed by bioelectrical impedance analysis (BIA) and muscle function by an isokinetic test.

Fifty-nine volunteers (47 years, 81.4% women) were recruited. Under fasting conditions, total body water, intracellular water (ICW), and extracellular water were positively correlated with knee flexion and extension strength, work, and power in men and women. The ICW to fat-free mass ratio and phase angle were positively correlated with flexion and extension strength and work in women but not men. Flexion strength and work improved significantly after water intake in women but not men. No changes in muscle function were observed in individuals younger than 45 years. In those aged 45 years or older, significant differences were observed for flexion strength (58.7 vs 61.8 N, p = 0.004), work (269.0 vs 284.0 J, p = 0.003) and power (39.5 vs 41.3 W, p = 0.018).

Hydration status appears to have a role in muscle function, especially with increasing age. More studies, however, are required to better understand the influence of hydration on muscle function and the underlying mechanisms.