Cardio is any form of exercise that raises your heart rate. There are a number of different cardio workouts to choose from, but given people’s hectic lifestyles, it's common to search for the one that elevates the highest possible fitness levels, promotes optimal fat burning, is the least time consuming, and is somewhat enjoyable. This difficult search can cause a divide of opinion amongst gym-goers, who tend to have a strong favorite between either high-intensity interval training (HIIT) or steady state (SS) cardio workouts.
HIIT protocols have varied considerably but typically involve repeated brief sprinting at an all-out intensity immediately followed by low-intensity exercise or rest. The length of both the sprint and recovery periods has varied from 6 seconds to 4 minutes.
SS typically describes exercise protocols performed continuously at a steady state for a set duration (usually 20 to 60 minutes). Intensities can vary but are usually moderate. Moderate-intensity activity is defined as an intensity that elicits a heart rate response of 55 to 69% HRmax or elevates the rate of oxygen consumption to 40 to 59% of VO2 max for a continuous period of time.
A meta-analysis (pool of studies that is applied to similar experiments) showed no evidence to support the superiority of either HIIT/SIT (sprint interval training) or SS for body fat reduction. Indeed, when interval training protocols were matched for energy expenditure/workload, similar benefits were observed. However, when comparing studies that employed HIIT/SIT interventions that incorporated less time and/or less energy expenditure than SS, there was a tendency to favor SS for total body fat reduction.
Fitness levels are typically assessed using the VO2 max test. VO2 max, also known as maximal oxygen uptake, is the measurement of the maximum amount of oxygen a person can utilize during intense exercise. It is one of several tests used to determine an athlete's cardiovascular fitness and performance capacity. HIIT has been shown to elicit greater VO2 max improvements compared to SS training. HIIT enhances both the anaerobic and aerobic system. Does this mean you should neglect endurance training? Absolutely not, as it primes the aerobic system and allows for better recovery.
Those who are focused on trying to get fitter faster and who want shorter workouts should look towards HIIT. If your goal is mainly to build muscle, then I would recommend minimizing HIIT to one or two sessions per week as it can affect recovery.
Those who want to reduce the risk of injury or are involved in a long-endurance event such as half marathon.
An ideal training environment would incorporate both sets of endurance training, but understand which form of training should be given more focus depending on the exercise intensity and duration you wish to compete in.
Steve O’Mahony, BSc MSc
Keating SE, Johnson NA, Mielke GI, Coombes JS. 2017. A systematic review and meta-analysis of interval training versus moderate-intensity continuous training on body adiposity. Obes Rev. Aug;18(8):943-964
Florian Azad Engel, Alexander Ackermann , Hamdi Chtourou and Billy Sperlich. 2018. High-Intensity Interval Training Performed by Young Athletes: A Systematic Review and Meta-Analysis. Front Physiol. Jul 27;9:1012