Author(s): ENDO, T., TANAKA, R., SUZUKI, S., KATO, Y., HAMAOKA-FUSE, S., KUROSAWA, Y., KIME, R., HAMAOKA, T., Institution: MEIJO UNIVERSITY, Country: JAPAN, Abstract-ID: 675

INTRODUCTION:
Prolonged sitting in daily life increases the risk of all-cause mortality and is associated with the morbidity of cardiovascular disease, cancer, and diabetes [1]. Although the underlying mechanisms are not fully understood, the acute impacts of prolonged sitting on human physiological parameters are a decline in lower-limb blood flow and vascular endothelial function, induced by gravity and reduced muscle activity during prolonged sitting [2]. However, it remains unknown whether reduced peripheral microcirculation in the lower limbs during prolonged sitting would change peripheral metabolic function. We therefore aimed to examine the effects of maintaining 3-h uninterrupted sitting (SiP), Fowler’s (FP), and standing positions (StP) on lower-limb muscle oxygen metabolism.
METHODS:
Seven healthy young participants (5 males and 2 females; age, 18.4 ± 0.7 yrs; body mass index, 18.8 ± 2.2 kg/m2) performed three posture maintenance experiments in randomized order on separate days. Each participant rested in a supine position for 30 minutes, followed by maintenance of 3-h uninterrupted SiP, FP, or StP. Muscle oxygen metabolism (resting metabolic rate, RMR) in the tibialis anterior (TA) and medial head of the gastrocnemius muscle (MG) was evaluated from the rate of decline in muscle tissue oxygen saturation (StO2) with an arterial cuff occlusion test using near-infrared spectroscopy [3]. Two-way repeated-measures ANOVA was used to compare the changes in RMR due to posture maintenance. For all statistical analyses, P < 0.05 was accepted as the level of significance. All data are expressed as mean ± standard deviation.
RESULTS:
In TA, the relative changes in RMR before and after the maintenance of SiP, FP, and StP were a 20.9 ± 11.7% reduction, a 28.7 ± 24.2% reduction, and an 8.1 ± 17.4% reduction, respectively. In MG, the changes in SiP, FP, and StP were a 21.9 ± 20.3% reduction, a 31.7 ± 18.0% reduction, and an 11.9 ± 18.5% reduction, respectively. There were no interactions between time (baseline vs. post) and posture for RMR in TA or MG (P = 0.11 and P = 0.22, respectively), whereas significant main effects for time were found in both TA and MG (P = 0.01 and P < 0.01, respectively).
CONCLUSION:
Maintaining 3-h uninterrupted SiP, FP, and StP significantly reduced lower limb muscle oxygen metabolism. In addition, the minor changes in RMR in StP, where muscle activation in TA and MG is assumed to be greater, suggest that intermittent muscle contractions during posture maintenance may prevent the decline in muscle metabolism.
REFERENCES:
1) Biswas A et al., Ann Intern Med, 2015.
2) Padilla J & Fadel PJ, Am J Physiol Heart Circ Physiol, 2017.
3) Hanna R et al., Physiol Rep, 2021.