PMID 42071842

Research
All papers

Combined low-volume high-intensity interval training and inspiratory muscle training in patients with metabolic syndrome: A randomized controlled trial

Uyar H, Vardar-Yagli N, Saglam M, Calik E, Uyaroglu OA, Ozdede M, Durusu Tanriover M

Question

Does adding inspiratory muscle training to an 8-week low-volume HIIT programme produce greater improvements in cardiorespiratory fitness, metabolic syndrome parameters, and respiratory muscle function than low-volume HIIT alone in adults with metabolic syndrome?

Summary

In a randomized controlled trial of 38 adults with metabolic syndrome, participants were assigned to treadmill low-volume HIIT, low-volume HIIT plus inspiratory muscle training, or a lifestyle-advice control for 8 weeks. Both exercise groups performed 26-minute supervised treadmill HIIT sessions three times per week, using six 1-minute intervals at 90-100% VO2max with 2-minute active recoveries. VO2max, several cardiometabolic markers, and metabolic syndrome z-score improved in the exercise groups, while respiratory muscle strength and endurance improved mainly when inspiratory muscle training was added. One participant withdrew because of knee pain and no serious adverse events were reported.

Methodology

  • Clinically stable adults with metabolic syndrome.
  • 38 participants.
  • Treadmill aerobic intervals; LVHIIT+IMT group also used inspiratory muscle training device.
  • Work intervals: 1 minute at 90-100% VO2max.
  • Recovery: 2 minutes active recovery at 50-70% VO2max.
  • Intensity: Warm-up/cool-down 30-50% VO2max; intervals 90-100% VO2max; recovery 50-70% VO2max; IMT 50% MIP.
  • 26 minutes for LVHIIT; IMT session duration not reported.
  • 3 LVHIIT sessions/week; IMT twice daily for LVHIIT+IMT.
  • 8 weeks.
  • Interventional, parallel-group, randomized controlled, double-blind trial with three groups: LVHIIT, LVHIIT plus IMT, and control.
  • VO2max, Metabolic syndrome severity, Anthropometrics and body composition, and Cardiometabolic blood markers were tracked.

Outcomes

VO2max

VO2max in mL/kg/min increased in LVHIIT from 15.57 +/- 4.78 to 19.98 +/- 4.40 and in LVHIIT+IMT from 16.26 +/- 3.77 to 20.57 +/- 1.85, with no change in controls.

Group x time P = .005 for VO2max mL/kg/min; within-group P = .001 for LVHIIT and P = .002 for LVHIIT+IMT.

Improved

MetS z-score

MetS z-score decreased from 4.55 +/- 4.30 to 0.10 +/- 2.50 in LVHIIT and from 3.17 +/- 2.73 to -0.95 +/- 2.65 in LVHIIT+IMT, with little change in controls.

Group x time P = .000.

Improved

Body composition and anthropometrics

Significant group x time interactions were observed for body weight, BMI, visceral fat ratio, waist circumference, and hip circumference; waist circumference decreased in both exercise groups but not control.

Group x time P values: body weight .016, BMI .039, VFR .015, waist circumference .014, hip circumference .006.

Improved

Glycemic markers and DBP

Fasting plasma glucose, HbA1c, and resting diastolic blood pressure improved in exercise groups, with no significant control change.

Group x time P values: FPG .010, HbA1c .018, DBP .040.

Improved

Respiratory muscle performance

MIP, MEP, and respiratory muscle endurance improved significantly only in the LVHIIT+IMT group.

Group x time P values: MIP .049, %MIPpred .001, MEP .038, respiratory muscle endurance .000.

Improved

Adherence and adverse effects

All participants completed at least 87.5% of sessions; one participant withdrew due to knee pain and no serious adverse events were observed.

Mixed

Insights

  • A six-by-one-minute LVHIIT protocol performed three times weekly can improve short-term VO2max in supervised adults with metabolic syndrome.
  • A total weekly LVHIIT time of about 78 minutes including warm-up and cool-down may be effective for short-term cardiometabolic improvements.
  • Adding IMT appears most relevant for respiratory muscle outcomes, not clearly for additional VO2max gains.
  • For app translation, VO2max intensity targets need practical alternatives such as RPE or heart-rate zones.

Limitations

  • Small sample size.
  • Predominantly female sample limits generalizability to male patients with metabolic syndrome.
  • No IMT-only group, so independent IMT effects cannot be determined.
  • Short 8-week intervention.
  • No long-term follow-up.
  • Many outcomes are surrogate markers rather than clinical events.
  • Supervised treadmill setting limits direct generalization to unsupervised or bodyweight-only HIIT.

Safety

  • One LVHIIT+IMT participant withdrew due to knee pain.
  • No serious adverse events were observed during or after training.
  • Participants were monitored by a physiotherapist during supervised sessions and instructed to report symptoms or unusual events.