The effect of sitting and calf exercise on fluid accumulation below the knees (1156.13)

Abstract

Background: Overnight rostral fluid shift from the legs to the neck correlates with the severity of obstructive sleep apnea (OSA) and time spent sitting. Sitting causes gravity‐dependent fluid accumulation in the legs that is counteracted by walking. However most office workers are required to sit for long periods and walking to preventing fluid accumulation in the legs is impractical. We hypothesized that sitting would cause fluid accumulation below the knees that could be attenuated by calf exercise while sitting.Methods: We measured fluid volume (FV) below both knees using bioelectrical impedance in 10 healthy subjects (8 men, age 50.8±6.2 yrs, BMI 23.7±2.4 kg/m2). Measurements were made in the supine, erect and seated postures and while sitting for 4 hours. Subjects were studied twice, a week apart, in a randomised double cross‐over design: control ‐ no calf exercise, intervention ‐ 15 calf muscle contractions against a pedal resistance (Step‐It) every 15 min. Paired t‐tests were used to analyze changes in FV and the effect of the intervention.Findings: Relative to the supine posture, FV below the knees increased in the erect (64.7±28.9 ml, p<0.0001) and seated postures (135.8.7±59.2 ml, p<0.0001) and after 4 hours of sitting (251.0±65.7 ml, p<0.0001). Modest exercise using the Step‐It device while sitting did not reduce fluid accumulation (control 115.2±47.0 ml, intervention 120.0±28.0 ml, p=0.72).Conclusions: Sitting for 4 hours results in substantial fluid accumulation in the legs of healthy subjects and this is not attenuated by modest intermittent calf exercise using a Step‐It device. This fluid could serve as a reservoir for redistribution to the neck and lungs during sleep, and contribute to OSA in predisposed individuals. A higher level of calf activity may be required to reduce fluid accumulation in the legs when sitting.