Greenfield recommends alternating these fast-twitch exercises with slow-twitch exercises throughout the week. The slow exercises can include long-distance jogging, walking, swimming, or lifting light weights.
On the HIIT days, he recommends doing 7- to 10-minute exercises, where you're moving very quickly and explosively, for 30 seconds on and 15 seconds off. Example moves include plyometrics, lunges, explosive pushups, etc. Here are a few HIIT workout routines for extra guidance.
Research has shown combing both types of exercise (and working out for at least 150 minutes each week) is the best way to support longevity. Endurance exercises, including HIIT programs, promote healthy aging by strengthening cardiorespiratory fitness. Strength training, even with light weights, can slow the loss of muscle mass, which naturally occurs in the aging process.