Sprint interval training (SIT)

Sprint interval training (SIT) is interval training built around all-out efforts.^{1Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 343.} ACSM distinguishes it from high-intensity interval training (HIIT), which uses vigorous efforts often near 60% to 89% of heart rate reserve.^{1Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 343.} SIT uses a workload or pace that produces responses from above 90% of heart rate reserve to 100% or more of peak oxygen uptake.^{1Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 343.} ACSM gives an example of three 20-second all-out intervals with 2 minutes of rest between them.^{2Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 344.}

The NSCA’s strength and conditioning text describes a comparable study under HIIT: four to six 30-second cycling sprints over six sessions produced the same gains in muscle buffering capacity and glycogen content as 90 to 120 minutes of continuous cycling at 65% of VO2 peak.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 76.} Time-trial performance improved 10.1% in the sprint group and 7.5% in the continuous-cycling group.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 77.}

In practice

• Rest length affects the adaptation: the NSCA reports that short rest between high-intensity sprints can improve VO2 max, while long rest improves sprint speed with little change in aerobic power.^{5Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 140.}
• Interval sprinting can suit most clients: sprint, run or walk as fast as ability allows, rest, then repeat.^{6Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 483.}
• Work at close to maximum speed to maintain sound mechanics, stride length and stride frequency, with enough recovery for a maximal effort on each rep.^{6Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 483.}
• The NSCA warns that combining HIIT with team practices can add stress and injury risk from overtraining.^{4Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 77.}