When creating the strength and conditioning routines of children it’s of paramount importance to ensure a healthy, and maximally productive program. Kids’ bodies are still in development, and they have busy schedules with limited time. It’s also harder to figure out if kids are overtraining, but more dangerous if they do. A recent study1 in The Journal of Strength and Conditioning Research compared the acute effects of a resistance training workout appropriate for children with a High Intensity Interval Training (HIIT) workout.
Boys and girls aged about 13 years old performed both a resistance training workout, and a HIIT workout in random order and separated by at least three days. They did a four week familiarization program where they got accustomed to the training and intensity levels used for the final workouts being tested. The workouts were time-matched, both with 30 seconds of work followed by 30 seconds of rest. The children were tested for their limits and their working sets for the test were submaximal.
The resistance training included pushups, squats and modified pullups (of the inverted row variety). They also occasionally performed other associated exercises during the familiarization phase, but everything was done with the body as the only source of resistance with one exception. Some of the stronger children used a sandbag to add resistance to the squats. They did four sets of 30 seconds for each exercise for a total of 12 sets (6 minutes of work).
The HIIT was performed on either an exercise bike or on a boxing bag. The kids learned a “non-contact” technique. They did 6 sets of each of these two exercises per workout for a total of 12 sets for the same duration as the resistance training.
The resistance training and HIIT both increased salivary cortisol levels (representing physiological and psychological stress) and blood lactate levels, although the HIIT increased the lactate levels higher. Average heart rate was about 9 beats per minute higher during the HIIT workout. The researchers determined that could have resulted from the horizontal position of two out of three of the resistance training exercises. The heart doesn’t need to work as hard when horizontal. They also indicated that the heart rate was still classified as “vigorous” despite the difference.
The substance Alpha Amylase was also studied to gain reference values for children, but the individual differences were too great to find anything useful there.
In terms of results, the HIIT received a stronger acute response across the variables, but the authors believe that the values were similar enough to represent a comparable training effect, especially since some of the differences between the two workouts could be explained merely by other confounding variables like what the kids ate that day, how well they slept, and so on.
Perhaps the most interesting part of this piece is the authors’ suggestion of applications. Assuming a safe resistance training program – a topic that is controversial already – the authors suggest the possibility that resistance training might be preferable in adolescents. They note that the cardiovascular response of the resistance training was similar to the high intensity interval training protocol, but that that resistance training has other benefits. Namely, they will also receive the neuromuscular benefits of resistance work, such as improved strength.
Photos courtesy of CrossFit LA Kids.
It’s also worth noting that two of the individuals didn’t have data in the HIIT training because the masks that provided the gas analysis for the study became too uncomfortable. However, they wore the same masks during the resistance training protocol. This might indicate that the HIIT itself was uncomfortable. The authors don’t discuss this issue at length, but as a coach, I find that people have a difficult time sticking with HIIT programs because of how unpleasant they feel. In support of this possibility, the children reported a higher perceived exertion during the HIIT training than the resistance training.
The authors drive the point home by stating that both the HIIT and the resistance training should be categorized as “vigorous” activity and there’s a limit to how much vigorous work a child should perform weekly. Since resistance training confers both cardiovascular benefits and improved strength, the workloads of children are perhaps better spent on resistance training.
1. Nigel Harris , et. al., “ACUTE RESPONSES TO RESISTANCE AND HIGH INTENSITY INTERVAL TRAINING IN ADOLESCENTS” Journal of Strength and Conditioning Research.