(35) SAME RESULTS, TWICE THE WORK? THE CARDIO-METABOLIC DIFFERENCES BETWEEN CIRCUIT TRAINING AND TREADMILL-BASED INTERVALS

While various methods of improving cardiovascular health exist, the workload and overall intensity to elicit similar aerobic adaptations may differ. For instance, resistance training often requires a greater anaerobic demand to evoke an oxygen consumption (VO₂) similar to low-to-moderate intensity aerobic activities (e.g., running). Thus, improving cardiovascular health, effectively and efficiently, requires an understanding of how various modes of training alter the cardio-metabolic responses during exercise.

Purpose: To observe the cardio-metabolic differences between a bodyweight circuit and interval-based treadmill running.

Methods: Ten active males (n=5) and females (n=5) completed a graded exercise test, bodyweight circuit, and treadmill intervals on three separate days spaced 48 hours apart. On day one, a graded maximal exercise test was completed to determine peak VO₂ and heart rate maximum (HR_max). For day two, subjects completed a bodyweight circuit consisting of 10 alternating rounds of burpees and jump squats with a 1:1 work-to-rest ratio. Each round was performed for 30 s followed by 30 s of passive recovery. On the last day of testing, individuals completed treadmill intervals set at a speed to match their average VO₂ obtained during the circuit. The work-to-rest ratio and number of rounds for the treadmill intervals were consistent with day two. During each session, blood lactate and glucose were measured via finger prick pre- and post-exercise, while VO₂ and HR were measured using a metabolic cart and heart rate strap, respectively. Within-group differences in VO₂, HR, lactate, glucose, respiratory exchange ratio (RER), and aerobic energy expenditure (kcals) were assessed using Friedman’s repeated measures ANOVA along with Cohen's d repeated measures effect sizes (d_rm) to determine the magnitude of effect between trials.

Results: Despite a matched average VO₂ between exercise sessions (d=0.05), circuits produced an average HR of 153±13 bpm (81.7±7.08 %HR_max) compared to an average HR of 147±12 bpm (78.12±5.94 %HR_max) (d=0.33) for the intervals. Moreover, circuit training exhibited a very large practical change in anaerobic energy contribution via lactate production (Δ 8.86±2.39 mmol/L) versus treadmill intervals (Δ 1.81±2.21 mmol/L; d=2.69). Anaerobic contributions are further demonstrated within the large practical difference in average RER between circuits (1.15±0.15) and intervals (0.98±0.06; d=1.54). Small effects were also observed in the mean change of blood glucose from pre-to-post exercise between the circuit (Δ 3.50±27.71 mg/dL) and intervals (Δ -7.55±39.53 mg/dL; d=0.32). Lastly, results indicated an average difference in aerobic caloric expenditure of 4.95±6.16 kcals (d=0.80) between the two modes favoring the resistance training circuit.

Conclusions: While matched for VO₂ output, bodyweight circuits required a greater anaerobic energy demand to elicit the same aerobic response achieved during treadmill intervals. These findings are consistent with previous literature demonstrating moderate %VO_2max values during a circuit, despite a high %HR_max and large practical change in blood lactate. PRACTICAL APPLICATIONS: Sedentary individuals seeking improvements in cardiovascular health or anaerobic capacity may opt for either circuit training or treadmill intervals. However, for moderate-to-highly trained subjects, circuit training may not elicit a great enough aerobic stimulus to warrant cardiovascular adaptations. 

Acknowledgements: None