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Can variable-intensity intervals increase your VO2 max?

A new study shows promising data

Some workouts may vary the intensity from interval to interval, but during each bout of hard cycling, you’re typically trying to maintain a steady pace throughout. Scientists from the University of Kent, however, found that by varying your intensity during the interval, you can spend more time at your VO2 max without making the workout itself feel any harder.

VO2 max

Your VO2 max is defined by the maximum volume of oxygen per minute that you can capture from the air, fix at pulmonary level, transport, and use. Once the muscular demand for oxygen is higher than your cardiovascular system’s ability to deliver it (above its maximum) your body switches from aerobic to anaerobically fueling, which is only sustainable for very short periods.

VO2 max intervals range from about two to eight minutes and will typically have riders working somewhere between 110-120 per cent of their functional threshold power (FTP).

RELATED: Which FTP test should you do?

Variable-intensity intervals

For the variable-intensity intervals study, which was published in the International Journal of Sports Physiology and Performance, the researchers created and tested a workout consisting of six, five-minute intervals separated by 2.5 minutes of active recovery. In the first session, the cyclists performed each interval at about 80 per cent of their maximal aerobic power (MAP) and each interval was done at a consistent pace. In the second session, they lowered the intensity to about 77 per cent of their MAP, but within each bout of hard cycling, they added in three, 30-second surges at 100 per cent effort.

Participants warmed up (A) then either went into (B) varied-intensity work intervals or (C) constant-intensity work intervals. image: Bossi et al.

14 trained cyclists completed the two workouts, and on average, they spent 6:50 above 90 per cent of their VO2 max during the variable-intensity workout, compared to 4:46 in the steady-intensity workout. Interestingly enough, when the athletes were asked to rate the difficulty of the two workouts, they rated them almost equally, despite spending more time at a higher percentage of their max in the second workout. That means they got a greater physiological benefit without making the workout psychologically any harder.

Should you modify your workouts?

In their study the researchers note that “whether performance adaptations will be superior to constant-intensity work intervals remain to be established by a longitudinal study,” but, similar respiratory frequency, HR, blood lactate concentration, ratings of perceived exertion, and training load metrics suggest that “it is unlikely that negative training outcomes occur.”

A version of this article originally appeared in Canadian Running Magazine