Making a HIIT: Methods for quantifying intensity in high-intensity interval training in schools and validity of session rating of perceived exertion

Figures & data

Table 1. Classes involved in the high-intensity interval training (HIIT) intervention.

School	Class	Year	Age^⍦	N (female)*	Number of HIIT workouts with HR data	Number of HIIT Workouts Completed by Students^⍭
School One	Class A	8	13.3 ± 0.3	25 (11)	8	8 (7 to 8)
	Class B	8	13.2 ± 0.4	12 (6)	8	7 (6 to 7)
School Two	Class C	7	12.6 ± 0.3	24 (0)	6	4 (3 to 5)
	Class D	7	12.5 ± 0.3	23 (0)	7	5 (5 to 7)
	Class E	8	13.6 ± 0.4	24 (0)	7	5 (3 to 7)
	Class F	8	13.7 ± 0.3	24 (0)	11	9 (5 to 10)
School Three	Class G	8	13.4 ± 0.3	21 (21)	6	5 (4 to 5)
	Class H	8	13.3 ± 0.3	23 (23)	5	3 (3 to 5)
	Class I	7	12.4 ± 0.3	19 (19)	4	3 (3 to 4)
	Class J	7	12.5 ± 0.3	18 (18)	6	5 (3 to 5)

^⍦Mean and standard deviation for normally distributed variables.

*N = the number of students with valid heart rate data included from each class.

^⍭Median and Interquartile range for not normally distributed variables.

HIIT = high-intensity interval training; HR = heart rate.

Figure 1. A) the average heart rate (percentage of heart rate maximum) across the intervention for students in a single class. B) the average heart rate (percentage of heart rate maximum) for each week of the intervention. It decreased on average 0.6% each week (p < 0.001). C) the peak heart rate (percentage of heart rate maximum) for each week of the intervention. It decreased on average 0.5% each week (p < 0.001).

Table 2. Intensity of high-intensity interval training (HIIT) workouts using various heart rate quantifications and session rating of perceived exertion.

Quantification of Intensity	Full Sample (n = 213)	Males (n = 115)	Females (n = 98)
Average HR^⍭	161 bpm (16 bpm)	162 bpm (5 bpm)	159 bpm (19 bpm)
Average HR as a percentage of HR maximum^⍭	79% (8%)	79% (7%)	79 (9%)
Peak HR^⍭	188 bpm (13 bpm)	188 bpm (12 bpm)	186 bpm (16 bpm)
Peak HR as a percentage of HR maximum^⍭	92% (6%)	92% (5%)	93% (7%)
Percentage of time between 70–79% of HR maximum^☨	26% (IQR: 14% − 37%)	26% (IQR: 16% − 37%)	25% (IQR: 11% − 37%)
Percentage of time between 80–89% of HR maximum^☨	38% (IQR: 22% − 52%)	38% (IQR: 23% − 52%)	36% (IQR: 20% − 54%)
Percentage of time between 90–100% of HR maximum^☨	6% (IQR: 0% − 23%)	5% (IQR: 0% − 21%)	7% (IQR: 0% − 26%)
Percentage of students with an average HR > 80%^⍦	51% (IQR: 31% − 67%)	50% (IQR: 30% − 67%)	55% (IQR: 40% − 70%)
Percentage of students with an average HR > 90%^⍦	5% (IQR: 0% − 8%)	0% (IQR: 0% − 7%)	0% (IQR: 0% − 13%)
Percentage of students where (Time with HR > 80%) ≥ (Time in work)^⍦	38% (IQR: 20% − 58%)	36% (IQR: 18% − 55%)	47% (IQR: 23% − 60%)
Percentage of students where (Time with HR > 90%) ≥ (Time in work)^⍦	0% (IQR: 0% − 6%)	0% (IQR: 0% − 5%)	0% (IQR: 0% − 7%)
Average rating of perceived exertion^⍭^✶	6 (2)	6 (2)	6 (2)

HR = Heart rate; bpm = beats per minute.

^⍭Mean and standard deviation across all students and sessions.

^☨Median and IQR across all students and sessions.

^⍦Median and interquartile range (IQR) within a class.

✶ Using the omnibus children’s rating of perceived exertion scale, which ranges from 0–10 points.

Figure 2. The within-person correlation between training impulse calculated with Edwards method using heart rate and session rating of perceived exertion.