Abstract: To evaluate if resistance training can reach Moderate to Vigorous Intensity (MVI) and contribute to the aerobic component of the international physical activity guidelines. Sixteen participants aged between 20 and 35 were recruited. Heart rate was recorded by heart rate monitor during a resistance training program. Based on maximal heart rate, time spent at MVI (55-69% of maximal heart rate) was calculated. Participants displayed a HR equal or above MVI for 51.5% ± 21.7% of time. When stratifying by lower and upper body sessions, that proportion was median (25-75th); 75.0% (32.5%-89.2%) and 45.8% (30.0%-66.8%) respectively. Body mass (r=.68; p<.01), body mass index (r=.54; p=.03), and leg press strength (r=.59; p=02) were positively associated with time spent at MVI. Assuming 10-minute bouts of aerobic exercise are not needed to achieve health benefits, it is possible to reach MVI with resistance training. Emphasis on the importance of performing resistance training should be done to reach the aerobic component of the physical activity guidelines and optimize health benefits. This provides an alternative option to those who may have difficulty or be unable to reach the required aerobic intensity by traditional aerobic exercises.
Alex’s Notes: I was pleasantly surprised to come across this study. Dedicated cardiovascular training has seemed to take a beating in the resistance training world. I could be wrong and oblivious, but it appears that most forgo cardio when looking to gain muscle and strength (which makes sense), but also when looking to shed some fat. I am definitely one of those people, although I do walk 5-6 miles daily. Anyway, the purpose of the current study was to see how much of the time spent doing resistance training would qualify as moderate-to-vigorous aerobic activity (MVI; greater than 55% of age-predicted maximum heart rate).
Thirty-nine participants who had been doing regular resistance training for the past two years (self-reported) underwent a nine week resistance training program, of which 16 wore a heart rate monitor for at least two training sessions and were included for analysis. Given the goal of the study, it doesn’t make much sense that all the participants were not required to wear a heart rate monitor for every training session, and this limitation will become apparent in a moment. Of the 16 persons, five (31%) were males, the average age was 28-years and the average DXA confirmed body fat was 28%.
The resistance training program appears in the table below, and every week each participant completed four workout sessions in an upperbody / lowerbody split with at least two days of rest. They performed three sets of 12,10,8 repetitions on all exercises except the abdominal crunch that was performed until failure, had rest periods of 90-120 seconds, and were required to lift 80% of their 1RM, which was calculated by having them lift a weight one to ten times until failure and then converted to the corresponding 1RM value using a percentage table.
The workout sessions lasted an average of 38 minutes, and there is no data mentioned as to whether the nine week routine increased strength or muscle mass, which doesn’t really matter, provided the aim of the study, but is still interesting data that was left out. Speaking of study aims, over the entire nine week program that consisted of roughly 36 workout sessions for which data could have been acquired; the average heart rate monitor duration was for four (11%) sessions.
Half the time of the workout sessions was spent in MVI, with that value increasing to 75% during lowerbody workouts and decreasing to 45% during upperbody workouts. However, the difference between the upper/lower sessions only tended towards significance (p=0.07), which is likely the result of the low sample size and limited number of data points. It should also be noted that the time spent in MVI ranged from 32-90% on lower body days and from 30-67% on upperbody days. Both body mass and BMI were significantly associated with the percentage of time spent in MVI, as were handgrip strength and leg press 1RM.
This makes sense when we consider that greater bodyweight means greater loads that must be moved and supplied with blood. Similarly, most people are much stronger in their legs than upperbody and thus must lift more weight and exert more force to apply the same stimulus to the working muscles. Yet, although the stimulus to the muscles is relatively the same, the systemic effects of lifting greater loads are more pronounced, which explains why more time on leg days was spent in MVI.
So while oxygen consumption measurements are preferable to heart rate monitoring for determining exercise intensity, and the statistical power of the study was greatly impeded by poor internal design, just know that about half of your workout time is helping you work towards the recommended 150 minutes of moderate-to-vigorous aerobic physical activity.