The Optimal Method of Hill Interval Training: Continuous versus Random

Abstract

The American College of Sports Medicine and the American Heart Association recommend that healthy adults, under 65 years of age, complete 20 minutes of vigorous cardiovascular exercise three times per week. A simple and convenient method of performing this exercise requirement is walking outside or on a treadmill while incorporating hills to increase the intensity. However, it is unknown how the hill intervals should be implemented, as longer continuous intervals or shorter random intervals, in order to maximize the cardiovascular benefits and calorie expenditure. PURPOSE: To determine whether a continuous or random hill walking protocol, with equal mechanical workloads, yields a greater metabolic cost. METHODS: Ten participants, 5 men and 5 women, completed 2, 20-minute walking protocols: long, continuous hill intervals and short, random hill intervals. Both protocols were performed on a treadmill at 2.0 m/s with 5 different inclines of 0, 6, 12, 18, and 24 percent grade. Each protocol included the same amount of time at each incline and the same amount of time transitioning between inclines. The continuous protocol was a combination of 5, 192-second hill intervals with 4, 60-second transition intervals. The random protocol was a combination of 20, 48-second hill intervals with 20, 12-second transitions. Both the order of the protocols and the order of the inclines differed between participants. We measured metabolic cost, lower limb kinematics, and leg muscle activity and statistically compared the two protocols using a paired t-test. RESULTS: Metabolic cost was greater during the continuous protocol in comparison to the random protocol for all ten participants (p = 0.007). On average, the participants expended 145 + 20 kcals during the continuous protocol and 131 + 20 kcals during the random protocol (mean + sd). Although the absolute number of calories appears inconsequential when evaluating a single exercise bout, the 10% greater cost of the continuous protocol could be substantial when summed over multiple bouts. CONCLUSION: When completing the recommended 20 minutes of vigorous cardiovascular exercise, a protocol that involves longer hill intervals would be optimal in terms maximizing metabolic cost and therefore the number of calories expended.