Breaking up sedentary time, physical activity and lipoprotein metabolism.

OBJECTIVES: Some authors report delayed responses of lipid metabolism after prolonged and interrupted sitting. To date no experimental studies have shown acute physical activity (PA) related changes of lipoprotein metabolism during sedentary behavior (SB). The purpose of this study was to examine immediate effects of a single PA-bout vs. regular PA-breaks on lipoprotein metabolism during postprandial SB.

DESIGN: Eighteen female subjects (25.6years±2.6; 21.5kg/m2±2.0) participated in a balanced crossover experiment with three trials: (1) 30min PA prior to 4h sitting (PRE), (2) 5×6min PA within 4h sitting (BREAK) (3) 4h sitting (CTRL). PA was ergometer cycling at 70%VO2 max. Participants consumed one standardized breakfast in each trial.

METHODS: Total cholesterol (tChol), high density lipoprotein (HDL), low density lipoprotein (LDL) and triacylglycerol (TAG) readings were taken in fasted state at the beginning (before), and immediately after each trial. Multiple 2×3-ANOVAs (trial-arm*time) and post hoc t-tests were used.

RESULTS: ANOVAs revealed trial*time-effects for tChol (p=0.043) and HDL (p=0.007) and a tendency for LDL (p=0.078). Before-to-after differences (Δ) of tChol during BREAK-trial (-0.89±5.49mg/dl) significantly differed to Δ during PRE-trial (+3.56±5.32mg/dl) (p=0.005) but not to ΔCTRL (+2.16±8.72). ΔHDL during BREAK-trial (-2.11±3.31mg/dl) significantly differed to ΔPRE (+0.83±4.26mg/dl) (p=0.007) and ΔCTRL (+0.06±4.15mg/dl) (p=0.028). Analysis of TAG revealed a time effect (p=0.007) and significant differences between TAG before and after trial within BREAK (79.22±38.69mg/dl to 94.78±44.86mg/dl) and CTRL (80.94±32.94mg/dl to 97.72±41.19mg/dl) but not in PRE (78.83±33.13mg/dl to 89.06±33.83mg/dl).

CONCLUSIONS: Breaking sedentary behavior with vigorous intensity PA seem to decelerate postprandial lipoprotein metabolism during sitting. In contrast, prior PA, might be a stimulus for lipid metabolization.