The aim of this study was to apply an SDT framework to investigate the effects of HIIT on children’s MVPA, enjoyment, and perceived competence during elementary PE classes. We assessed these relationships during one week of a year-long PE intervention. Overall, children tended to enjoy HIIT in both conditions and to perceive themselves as competent with scores consistently above 4.0 on the 5-point Likert-type scale. Neither enjoyment nor competence were impacted by grade or sex – with 2nd − 5th grade male and female students rating the HIIT conditions largely similarly. Thus, regardless of age and sex, elementary students appear to enjoy HIIT activities as used in this study and to feel competent in executing these activities. However, there were differences as a function of sex based on conditions. Both male and female students rated autonomous HIIT lessons more enjoyable than non-autonomous, and males enjoyed the non-autonomous condition more than female students. Females’ enjoyment rating of HIIT in the non-autonomous condition was the only instance with a rating below 4.0 (3.95) on the 5-point Likert-type scale. Students also had significantly higher ratings of perceived competence for HIIT in the autonomous condition compared to the non-autonomous, which was not impacted by gender or sex.
In contrast to children’s experience with and perceptions of HIIT, percent of time in MPVA was significantly lower in the autonomous condition compared to the non-autonomous condition, which was affected by grade and sex. While all sexes and grades revealed higher percent MVPA during HIIT in the non-autonomous condition compared to the autonomous, 4th grade students had lower percent MVPA in the autonomous condition compared to all other grades. Females across grades also had lower percent MVPA during HIIT in the autonomous condition compared to males. This pattern of effects suggests a trade-off between psychological outcomes (enjoyment and perceived competence) and health-related outcomes (intensity of PA) within a HIIT protocol.
While children tended to enjoy and feel competence during both HIIT conditions, the preference for the autonomous protocol aligned with the principals of SDT [23], which is consistent with a long history of PE research. PE teachers are fundamental to facilitating autonomy and competency experiences for children that ultimately support students’ intrinsic motivation towards PA [38]. Teachers who support autonomy in their classroom have been associated with students who demonstrate increased motivation, classroom engagement, skill development, future intention to exercise, and academic achievement [39]. It is not surprising that children expressed more enjoyment and perceived competence during the lessons that provided a sense of choice. When PE teachers led the lessons, children had little control over the class. Rather than an intrinsic set of self-determined motives, this creates a setting that emphasizes other-determined (teacher) controlled motives for each activity [40]. Other-determined extrinsic motivators include fear, guilt, and obligation that are not autonomous because participants perceive an external source controlling their behavior [40]. Such perceptions have been found to lower motivation and adherence [40]. While the current study was unable to assess behavior over a long-course of time, it would be important to examine how PE teacher-controlled movements impact intentions to be active.
In contrast, the results revealed that intensity of activity significantly decreased with increased enjoyment and perceived competence in the autonomous condition compared to the non-autonomous condition. While enjoyment and perceived competence are important outcomes for promoting children’s lifelong PA participation [20], higher levels of MVPA in children are associated with better cardiometabolic risk factors outcomes including waist circumference, fasting insulin levels, BMI, and body fat [41, 42]. There is preliminary evidence suggesting that the more time children spend in activity in general – and vigorous activity in particular - the greater the reduction in several cardiovascular disease risk factors including BMI and waist circumference, and the greater improvements in cardiorespiratory fitness [43, 44]. Given these data, it is not surprising that HIIT, when offered at a sufficient dose, results in meaningful improvements in cardiorespiratory fitness, systolic blood pressure, vascular function, and resting metabolic rate compared to moderate intensity PA in children and adolescents [16–18]. According to our results, while fostering autonomous experiences increases children’s enjoyment, it seems to undermine intensity of activity – especially for female students. Therefore, both PE teachers and researchers face a challenge when attempting to balance enjoyment of HIIT and sufficient MVPA needed to improve fitness and other cardiovascular disease risks factors. This balance must be considered with future large-scale HIIT interventions designed for children especially in the school setting.
While this study was not designed to assess teacher preferences, it is interesting that the PE teachers expressed their concern with disruptive classroom behavior when providing autonomy and student choice during PE. The teachers explained that large class sizes within a small gym environment were not conducive to an autonomous HIIT protocol if sufficient intensity, form, and time-efficiency were to be achieved. As a result, the PE teachers only allowed students to participate in the non-autonomous HIIT condition during the PE warm-up for the remainder of the school year. Thus, while promoting autonomy is clearly beneficial for children’s motivation and experiences with PA [38], more research is required to better understand the challenge in managing the modern PE classroom and ensuring the needs of PE teachers are met within any intervention in the PE classroom.
There were key differences as a function of method of delivery. Because the conditions differed in who was selecting the activity (students vs teachers), there were observed variations in the activities selected. When the students selected the HIIT activities they tended to select aerobic and lower intensity activities like high knees, jumping jacks, straddle stretch, and child’s pose. In contrast, when teachers selected the HIIT activities they emphasized a routine of 7 high-intensity and strength based exercises interspersed with lower-intensity exercises. This different pattern of selection is sufficient to explain the observed differences in intensity between the autonomous and non-autonomous HIIT conditions. We do not have data to assess why children made these selections, e.g. due to differences in enjoyment of these activities or their perceived competence / ability across different tasks, or some other variable. Higher intensity activity has consistently shown to be associated with negative affect in adults [45] but there is less existing research with youth. Costigan and colleagues [46] recently found that higher levels of vigorous activity were associated with more positive affect and less negative affect in a large sample of adolescents – which appear in contrast to the data for adults. However, affect and intensity have yet to be explored in elementary-aged children. Such data may help to explain the preference for HIIT activities. Further, we know of no work that has assessed differences in perceived competence at activities of different intensities among children. It is reasonable to expect that the physiological response to intense activity might be associated with perceptions of poor performance, especially for those who are less experienced with high intensity activity or have lower cardiorespiratory fitness [15]. It may be that more exposure to and training in higher intensity activities perhaps with an impact on fitness, would serve to reduce the differences in the selection of these activities when given choice. This is clearly an area ripe for future study.
Limitations
The current study has several shortcomings. While the sample was large and fairly diverse, this study took place at one school with the 3 PE teachers, limiting generalizability to other schools. We also did not have the measures to establish that the participant’s heart rate and/or VO2max to ensure the HIIT stimulus classification of greater than or equal to 70% VO2peak or the equivalent of HRmax was achieved [25]. Our measure of intensity was limited to those participants who wore GTX3X + accelerometers. These data indicated that we did not achieve true high intensity PA during HIIT, reducing the potential benefit of the selected HIIT intervention. This is in part due to the challenge of working with a class of over 100 students – as made clear by the PE teachers. It is also a function of the activities selected by the students. Future research must consider how to achieve a more acceptable dose of HIIT within the constraints of the PE classroom and considering children’s preferences. Additionally, as data collection only took place over the course of 1 week per grade, the repeated measures design is subject to carry over effects from previous condition. However, limiting data collection to 1 week per grade likely helped prevent differential attrition and fatigue of participants. Lastly, neither students nor PE teachers were not able to be blinded to condition, which may have resulted in information bias.