The effects of two weeks high-intensity interval training on fasting glucose, glucose tolerance and insulin resistance in adolescent boys: a pilot study
Question
Do two weeks of supervised HIIT improve fasting and postprandial glucose and insulin outcomes in healthy adolescent boys, and are baseline insulin resistance, BMI, or aerobic fitness related to change in insulin resistance?
Summary
In a small uncontrolled pilot study, seven healthy 14-year-old boys completed six supervised cycle-HIIT sessions across two weeks. The intervention did not improve fasting glucose, fasting insulin, insulin-resistance indices, postprandial glucose or insulin responses to a mixed meal, or VO2max at 20 hours or 70 hours after the last session. A strong correlation suggested boys with higher baseline insulin resistance may have improved more, but the sample was too small for firm conclusions.
Methodology
- Healthy year 10 adolescent boys from a local secondary school; three of seven completers were classified as overweight.
- 7 participants.
- Cycle ergometer.
- Work intervals: 1 min at 90% peak power from incremental ramp test.
- Recovery: 75 s unloaded pedalling.
- Intensity: 90% of peak power; self-selected cadence 70-95 rev/min.
- Approximately 27-33 min depending on interval count, including 3 min warm-up and active recoveries.
- 3 supervised sessions/week.
- 2 weeks.
- Uncontrolled within-subject pilot intervention with pre/post laboratory assessments.
- Fasting glucose and insulin, Insulin resistance and sensitivity indices, Postprandial glucose and insulin response, and VO2max and aerobic fitness were tracked.
Outcomes
Fasting glucose, insulin, and insulin-resistance indices
Two weeks of HIIT did not change fasting glucose, insulin, HOMA-IR, HOMA-S%, HOMA beta%, QUICKI, or FGIR at 20 h or 70 h after the final session.
All repeated-measures ANOVA P values > 0.05; examples: glucose P=0.86, insulin P=0.84, HOMA-IR P=0.85.
Mixed Meal Tolerance Test glucose and insulin responses
No significant changes were observed for glucose iAUC/tAUC or insulin iAUC/tAUC after the mixed meal.
Glucose iAUC P=0.57, glucose tAUC P=0.56, insulin iAUC P=0.78, insulin tAUC P=0.60.
VO2max and fitness markers
VO2max changed from 2.44 +/- 0.70 to 2.52 +/- 0.76 L/min and was not statistically significant; HRmax, GET, and peak power were also not significant.
VO2max P=0.27; HRmax P=0.65; GET L/min P=0.85; GET percent VO2max P=0.60; peak power P=0.09.
Baseline insulin resistance relationship
Higher baseline insulin resistance was strongly associated with greater reduction in HOMA-IR after the intervention.
r = -0.96, P < 0.05.
Physical activity and diet standardization
Moderate-vigorous physical activity and estimated energy/macronutrient intake in the 48 h before each visit did not differ significantly.
All P > 0.05; MVPA P=0.55, total energy intake P=0.71.
Insights
- A six-session, two-week HIIT block should not be presented as enough to improve glucose or insulin outcomes in healthy adolescent boys.
- Baseline insulin resistance may be a better targeting criterion than BMI for youth metabolic HIIT interventions.
- School-based supervised lunch-break HIIT can use short progressive cycle sessions, but the evidence here is mainly useful as a caveat because primary outcomes were null.
Limitations
- No control group.
- Very small pilot sample.
- Male-only adolescent sample.
- Mixed Meal Tolerance Test may have reduced comparability with studies using oral glucose tolerance tests.
- Healthy participants may have had limited room for metabolic improvement.
- Exact intervention translation requires cycle ergometer and peak-power testing.
Safety
- No intervention-related adverse events were reported in the the paper.
- One recruited boy failed to complete HIIT due to unrelated illness.
- One recruited boy could not complete training due to unrelated injury.
- Participants were screened by health questionnaire to exclude exercise contraindications and conditions affecting glucose metabolism.