Sitting, standing or breaking: Which is better for cardio-metabolic health? A randomised cross-over study

INTERVENTION: Participants will complete, in a random order, two intervention session and one control session. Each session will be separated by six days. The two intervention sessions are as follows: 1) Regular activity breaks: Participants will walk on the treadmill at 5 km/h for 2 min every 30 min throughout the 6.5 h intervention session. At all other times they will remain seated 2) Continuous standing: Participants will stand at a standing desk continuously throughout the 6.5 h session. The control session is: Continuous sitting, in which the participant will remain seated for the duration of the session. During each intervention/control session participants will be fed a standardised breakfast (of Muesli, milk, toast, margarine, honey and juice providing 106 g of carbohydrate and 13 g fat) at 45 min, and a standardised snack (chocolate brownie, providing 44 g carbohydrate and 17 g fat) at 240 min. Investigators will be in the laboratory with participants at all times to ensure compliance to these procedures CONDITION: Cardiovascular ‐ Diseases of the vasculature and circulation including the lymphatic system Diet and Nutrition ‐ Other diet and nutrition disorders Metabolic and Endocrine ‐ Metabolic disorders Prolonged sitting;Postprandial glycemia;postprandial insulinemia ;endothelial function; ; Prolonged sitting ; Postprandial glycemia ; postprandial insulinemia ; endothelial function PRIMARY OUTCOME: Flow‐mediated dilation will be measured by inducing transient ischema by inflating a 12 cm cuff around the mid‐calf 200 mm Hg within 2 seconds (SC12 contoured leg cuff, E20 Rapid Cuff Inflator and AG101 Cuff Inflator Air Source, Hokanson, Bellevue WA, USA). Occlusion will be maintained for 5 min and recording will be continued for 3 min following rapid release of the cuff. Baseline diameter (Dbase), blood flow velocity (v) and shear rate (SR) will be calculated as the mean of the last minute of recording prior to cuff inflation. Peak diameter post‐deflation will be determined automatically using the edge‐detection software. Flow‐mediated dilation will be calculated as the percentage increase in diameter from the baseline (FMD = (Dpeak‐Dbase) / Dbase x 100), following guidelines utilising allometric scaling to adjust for Dbase with a covariate‐controlled approach[Measurements will be performed at the beginning and end of each intervention session (0 and 390 min)] 60 seconds on each occasion.[Measurements will be performed baseline, and at even intervals throughout the intervention ( 0, 60, 120, 180, 240, 300, 360, 390 min)] The glucose profile for the 48 h following each intervention session will be assessed using a Freestyle Libre glucose monitoring sensor worn continuously on the back of the upper arm[48 h following each intervention session] INCLUSION CRITERIA: Healthy men and women who self report spending greater than 5 h per day, on average, engaged in sedentary behaviour, and who do not use a sit to stand work station or standing desk on a regular basis. SECONDARY OUTCOME: Physical activity patterns will be assessed for 48 h after each intervention using an Actigraph accelerometer worn continuously on the right hip, and established cutoffs for sedentary, light and moderate‐to‐vigorous physical activity patterns[48 h after each intervention/control session ] Postprandial glucose response will be assessed by collecting blood samples at the time points listed below, and using them to calculate incremental area under the curve. Concentrations of glucose will be measured in each sample using enzymatic calorimetric methods[Measurements will be performed baseline, and at even intervals throughout the intervention ( 0, 60, 120, 180, 240, 300, 360, 390 min)] Postprandial insulin response will be assessed by collecting blood samples at the time points listed below, and using them to calculate incremental area under the curve. Concentrations of insulin will be measured in each of these samples using an electrochemiluminescent immunoassay[Measurements will be performed baseline, and at even intervals throughout the intervention ( 0, 60, 120, 180, 240, 300, 360, 390 min)] Superficial popliteal artery haemodynamics will be investigated by assessing popliteal artery (PoPA) diameter and blood velocity using ultrasound (Terason uSmart 3300, MA, USA) with a 15 MHz lineal array transducer (bandwidth 4‐15 MHz) by simultaneously recording a longitudinal section B‐mode image and a spectral Doppler trace of blood velocity. The Doppler angle of insonation will be maintained at less than or equal to 60°. Measurements will be made in the popliteal fossa with the participant in a semi‐recumbent position, in the prolonged sitting and regular activity breaks interventions, and in a standing position in the prolonged standing intervention. Video clips will be recorded using Camtasia Studio Screen Recording Software (TechSmith, MI, USA). Analysis of diameter and velocity, and calculation of shear rate will be performed using wall‐tracking software (Cardiovascular Suite v 3.4, Quipu, Pisa, Italy). Haemodynamics will be assessed for