PMID 34381998

Research
All papers

Short-Term, Equipment-Free High Intensity Interval Training Elicits Significant Improvements in Cardiorespiratory Fitness Irrespective of Supervision in Early Adulthood

Sian TS, Inns T, Gates A, Doleman B, Gharahdaghi N, Atherton PJ, Lund JN, Phillips BE

Question

Can a short, equipment-free bodyweight HIIT program improve cardiorespiratory fitness in young adults, and does supervision matter?

Summary

In 30 recreationally active young adults, 4 weeks of no-equipment bodyweight HIIT improved anaerobic threshold, VO2peak, BMI, and vastus lateralis pennation angle compared with no intervention. Improvements were similar whether sessions were supervised in the lab or performed unsupervised at home. One home participant was excluded for not completing enough sessions; otherwise adherence and target-HR compliance were reported as 100%, with no adverse events.

Methodology

  • Healthy, recreationally active, non-obese young adults aged 18-30 not engaged in a formal exercise regimen of 2 or more sessions per week.
  • 30 participants.
  • Star jumps, standing squats, and on-the-spot standing sprints.
  • Work intervals: 1 minute high-intensity effort.
  • Recovery: 90 seconds active recovery, plus 2 minutes after the final effort.
  • Intensity: Aim to achieve more than 85% age-predicted HRmax for each effort.
  • Less than 16 minutes for the HIIT session: 2-minute warm-up, 5 x 1-minute efforts, 90-second recoveries, 2-minute final recovery.
  • 3 sessions per week.
  • 4 weeks.
  • Three-arm randomized controlled trial
  • Anaerobic threshold, VO2peak, BMI, and Blood pressure were tracked.

Outcomes

Anaerobic threshold

Both supervised lab and unsupervised home HIIT improved anaerobic threshold versus control, with no difference between HIIT settings.

L-HIIT MD +2.1 ml/kg/min, p=.02; H-HIIT MD +3.01, p=.002; L vs H p=.41.

Improved

VO2peak

Both HIIT groups improved VO2peak versus control.

L-HIIT MD +2.94 ml/kg/min, p=.01; H-HIIT MD +2.55, p=.03; L vs H p=.73.

Improved

BMI

BMI decreased modestly in both HIIT groups versus control.

L-HIIT MD -0.43 kg/m2, p=.05; H-HIIT MD -0.51, p=.03.

Improved

Muscle architecture

Vastus lateralis pennation angle increased in both HIIT groups, while muscle thickness and fascicle length did not clearly change.

Pennation angle p<.001 in both HIIT groups.

Mixed

Blood pressure and glucose/insulin

No significant changes occurred in resting BP, glucose AUC, insulin AUC, or HOMA-IR.

No clear change

Adherence

After one home participant was excluded for insufficient sessions, training adherence and HR target compliance were otherwise reported as 100%.

Improved

Safety

No adverse safety events were reported during exercise testing or training.

No clear change

Insights

  • A short no-equipment bodyweight HIIT format can improve CRF in young adults.
  • Home delivery can work when users are oriented to the protocol and given clear HR/intensity targets.
  • The protocol's simplicity makes it directly relevant to timer-based app programming.
  • Metabolic and blood-pressure outcomes may need longer programs or higher-risk participants to change.

Limitations

  • Small volunteer sample with possible self-selection bias.
  • Only 4 weeks of training and no long-term follow-up.
  • Home HR compliance was self-reported using pulse oximetry rather than remotely verified HR monitoring.
  • Habitual physical activity was not objectively measured during the study.
  • Menstrual-cycle phase was not controlled.

Safety

  • No adverse safety events were reported in any group during exercise testing or training.
  • Participants were medically screened and instructed what to do if adverse symptoms occurred.
  • CPET included continuous heart rate, blood pressure, and pulse oximetry safety monitoring.