Interval training

Interval training alternates periods of higher- and lower-intensity exercise in one session.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 455.} With set work and rest periods, it can in theory let a client do more high-intensity work with the same or less fatigue than continuous training.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 75.} In an early running study, participants who covered 0.81 miles before exhaustion at a fast continuous pace covered 3.11 miles in 30 minutes at the same speed using a 1:1 work-to-rest ratio.^{2Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 75.}

The NSCA’s strength and conditioning text places interval work close to VO2 max, with work bouts of 3 to 5 minutes (or as short as 30 seconds) and equal rest for the 3 to 5 minute bouts.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 584.} ACSM describes 20 seconds to 4 minutes at 90% to 120% of VO2 max, followed by 60 seconds to 6 minutes of light to moderate effort.^{4Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 342.} Jack Daniels found that three runners and their coach all defined interval training differently; hard running and recovery were their only points of agreement.^{5Daniels, Daniels’ Running Formula, 4th ed., p. 96.}

In practice

• The NSCA’s personal training text recommends an aerobic base before intervals: it says a client should be able to hold the target intensity for roughly as long as the planned interval session lasts.^{1Schoenfeld and Snarr (eds.), NSCA’s Essentials of Personal Training, 3rd ed., p. 455.} Its strength and conditioning text calls interval work very stressful and recommends using it sparingly.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 584.}
• Hold the target pace.^{6Daniels, Daniels’ Running Formula, 4th ed., p. 98.} Daniels explains that running faster than VO2 max pace adds no time at VO2 max, and an overly fast first rep can slow later reps below the planned pace.^{6Daniels, Daniels’ Running Formula, 4th ed., p. 98.}
• For detrained clients, ACSM suggests alternating brisk walking with slower walking.^{4Ozemek et al., ACSM’s Guidelines for Exercise Testing and Prescription, 12th ed., p. 342.}
• A well-run interval program can improve VO2 max and anaerobic metabolism.^{3Haff and Triplett (eds.), Essentials of Strength Training and Conditioning, 4th ed., p. 584.}