Gist et al., Sprint Interval Training Effects on Aerobic Capacity: A Systematic Review and Meta-Analysis Journal of Sports Medicine

Sprint interval training (SIT) has gained significant attention as a time-efficient strategy for improving aerobic capacity. SIT is a training protocol involving repeated bouts of "all-out" sprints, typically lasting 30 seconds, interspersed with brief recovery periods. This article will examine the effectiveness of SIT, particularly concerning its impact on aerobic capacity, and explore its physiological underpinnings.

This meta-analysis highlights the effectiveness of SIT in enhancing VO2max, a measure that reflects the body's ability to utilise oxygen efficiently during exercise. Examining 16 randomised controlled trials, this paper concluded that SIT leads to a "small-to-moderate" improvement in VO2max. More specifically, this improvement translates to an average increase of 3.6 mL kg-1 min-1, or about an 8% enhancement. Notably, the authors emphasised that this magnitude of improvement is approximately equal to the gains observed with traditional endurance training, which typically involves longer durations of moderate-intensity exercise.

While traditional endurance training is known to elicit both central adaptations, involving changes in the heart and lungs, and peripheral adaptations, occurring in the muscles, the precise contribution of these adaptations to SIT's effectiveness requires further investigation. Some studies suggest that peripheral adaptations, such as enhanced skeletal muscle oxidative capacity, might play a more prominent role in the initial stages of SIT, while central adaptations might become more evident with continued training. This distinction highlights the possibility of optimising SIT protocols based on individual training goals and the duration of engagement in the training regimen.

Furthermore, the authors acknowledge certain limitations to the existing body of research on SIT. The majority of studies included in the meta-analysis involved young, healthy participants, with a mean age of 23.5 years. Therefore, the generalisability of these findings to older populations, such as Masters athletes, or individuals with underlying health conditions requires further investigation. Additional research is necessary to ascertain the safety and effectiveness of SIT in these populations, particularly considering potential age-related physiological changes and the presence of any health limitations.

Additionally, the long-term effects of SIT on VO2max and other health-related outcomes remain to be fully elucidated. Most studies employed training interventions lasting less than six weeks. Investigating the impact of prolonged engagement in SIT is essential to determine its sustainability and the potential for continued improvements in aerobic capacity over time. Moreover, exploring the long-term effects would shed light on the potential influence of SIT on other health markers, such as blood pressure, insulin sensitivity, and body composition.

In conclusion, the meta-analysis presents compelling evidence for the effectiveness of SIT as a potent and time-efficient method for enhancing VO2max, a key indicator of aerobic capacity and overall health. The findings suggest that SIT holds considerable promise as a valuable tool for improving cardiorespiratory fitness, potentially leading to greater levels of performance or greater training capacity.

Training Protcol

• Sprints: 4-6 repetitions of 30-second "all-out" sprints

• Intensity: Athletes should exert maximal effort during each sprint, aiming for "supramaximal" intensity

• Recovery: Allow for 4 minutes of recovery between sprints. This recovery period allows for adequate rest and facilitates optimal subsequent sprint performance.

• Frequency: Conduct SIT sessions 2-3 times per week. This frequency balances high-intensity training with sufficient recovery to maximise adaptations.

• Duration: Continue the SIT protocol for 4-6 weeks.

• Mode: While the research predominantly uses cycling for SIT, coaches can adapt the protocol to running, rowing, or other sport-specific activities to enhance transferability to competitive performance.

• Periodization: SIT is likely to be most effective early in the season for endurance athletes or can be included in the pre-competition phase for middle distance athletes.