Blood Glucose Response to Intermittent Posture Change and Light Activity During an 8hr Work Day

Abstract

INTRODUCTION: Prolonged sitting is associated with adverse cardio-metabolic outcomes. Reducing sitting time can improve blood glucose (BG); however, it is not clear whether this is due to changes in posture (i.e., more standing) or increases in light-intensity physical activity (i.e., greater energy expenditure). PURPOSE: To compare acute BG responses under four conditions: 1) sitting (SIT), 2) standing (STAND), 3) walking (WALK) and 4) cycling (CYCLE) during an 8hr work day. METHODS: Nine overweight (BMI= 29±3 kg/m2) adults (30±15 yr) with normal fasting BG levels (96±9 mg/dL) completed 4 conditions (SIT, STAND, WALK and CYCLE), randomly performed each week across four consecutive weeks. Participants wore a Medtronic IPro Continuous Glucose Monitor (CGM) across 3 days and BG levels recorded at 5-minute intervals, all meals were controlled during the testing period. STAND, WALK and CYCLE intervals were increased from 10 to 30 minutes (total of 2.5-hrs) across the 8hr work day. WALK (1.0 mph) and STAND (0.0 mph) were completed on a treadmill using a TREKDESK. CYCLE cadence and energy expenditure were controlled (equivalent to WALK) using a Monark cycle ergometer. Linear Mixed Models were used to test for condition differences in BG levels across a 24hr period (24HR), in the lab (LAB), in the evening (EVE) and during sleep (SLEEP). RESULTS: There was a 24HR mean BG treatment effect (P<0.01). Mean BG during STAND (100± 3.6mg/dL), WALK (97±3.6 mg/dL) and CYCLE (90±6.0 mg/dL) were lower compared to SIT (102±4.1 mg/dL) (P<0.01). There was a treatment effect during the intervention time (LAB P<0.01) and evening time (EVE P <0.01). Mean BG during STAND (LAB 97±4.4 mg/dL, EVE 101±4.4 mg/dL), WALK (LAB 94±5.0 mg/dL, EVE 100±5.0 mg/dL) and CYCLE (LAB 93±6.0 mg/dL, EVE 94±6.0 mg/dL) were lower than SIT LAB and EVE mean BG (102±5.0 mg/dL, 106±5.2 mg/dL respectively). Only the mean BG for CYCLE (88±3.3 mg/dL) remained significantly lower than SIT (101±3.3 mg/dL) during SLEEP (P<0.01). Mean BG within conditions was not significantly different between LAB, EVE, and SLEEP phases. CONCLUSION: Replacing sitting with regular intervals of standing or light-intensity physical activity (with or without additional standing) significantly reduces BG levels during and immediately following an 8hr workday.