Twelve Weeks of Sprint Interval Training Improves Indices of Cardiometabolic Health Similar to Traditional Endurance Training despite a Five-Fold Lower Exercise Volume and Time Commitment

Abstract

Aims: We investigated whether sprint interval training (SIT) was a time-efficient exercise strategy to improve insulin sensitivity and other indices of cardiometabolic health to the same extent as traditional moderate-intensity continuous training (MICT). SIT involved 1 minute of intense exercise within a 10-minute time commitment, whereas MICT involved 50 minutes of continuous exercise per session.

Methods: Sedentary men (27±8y; BMI = 26±6kg/m2) performed three weekly sessions of SIT (n = 9) or MICT (n = 10) for 12 weeks or served as non-training controls (n = 6). SIT involved 3x20-second 'all-out' cycle sprints (~500W) interspersed with 2 minutes of cycling at 50W, whereas MICT involved 45 minutes of continuous cycling at ~70% maximal heart rate (~110W). Both protocols involved a 2-minute warm-up and 3-minute cool-down at 50W.

Results: Peak oxygen uptake increased after training by 19% in both groups (SIT: 32±7 to 38±8; MICT: 34±6 to 40±8ml/kg/min; p<0.001 for both). Insulin sensitivity index (CSI), determined by intravenous glucose tolerance tests performed before and 72 hours after training, increased similarly after SIT (4.9±2.5 to 7.5±4.7, p = 0.002) and MICT (5.0±3.3 to 6.7±5.0 x 10-4 min-1 [μU/mL]-1, p = 0.013) (p<0.05). Skeletal muscle mitochondrial content also increased similarly after SIT and MICT, as primarily reflected by the maximal activity of citrate synthase (CS; P<0.001). The corresponding changes in the control group were small for VO2peak (p = 0.99), CSI (p = 0.63) and CS (p = 0.97).

Conclusions: Twelve weeks of brief intense interval exercise improved indices of cardiometabolic health to the same extent as traditional endurance training in sedentary men, despite a five-fold lower exercise volume and time commitment.

Fig 1. Effect of SIT and MICT on VO₂peak.

Measured at baseline (PRE), 6 weeks (MID), and 12 weeks (POST) in MICT, SIT and CTL. Values are means ± S.D. * p<0.05, vs. same group at PRE; # p<0.05, vs. same group at MID.

Fig 2. Effect of SIT and MICT on insulin sensitivity.

The change in insulin sensitivity (CS_I) over the 12-week intervention, measured from a 50-minute IVGTT in MICT, SIT and CTL. Closed circles denote individual responses. Values are means ± S.D. * p<0.05, PRE vs. POST.

Fig 3. Effect of SIT and MICT on skeletal muscle mitochondrial content.

Measured in muscle biopsy samples obtained from the vastus lateralis before (PRE) and 96 h after (POST) the 12-week intervention in MICT, SIT and CTL. Maximal activity of citrate synthase (A), individual changes in maximal activity of citrate synthase (B) and protein content of various subunits from complexes in the electron transport chain (C). Representative western blots are shown. Values are means ± S.D. * p<0.05, vs. same group at PRE; † p<0.05, vs. CTL at POST.