Evidence Trace, complete trial record
In plain terms
In plain terms: REHIT / Sprint Interval Training has some human trial evidence supporting it, but the evidence is not yet strong enough for EBL to call it established. It is worth knowing about and worth discussing with your clinician.
REHIT / Sprint Interval Training
B
Supported: a good trial, backed by more
The endpoint this grade is based on: Objectively measured functional outcome
The evidence as the record states it
Metcalfe et al. (European Journal of Applied Physiology, 2012; PMID 22124524): 29 sedentary adults, 6 weeks of REHIT or control; VO2max rose 15% in men and 12% in women. Cuddy et al. (International Journal of Environmental Research and Public Health, 2019; PMID 30736402): 32 inactive adults, 8 weeks; fitness rose 12% with REHIT and 7% with moderate continuous training. Hu et al. (Journal of Exercise Science and Fitness, 2025; PMID 40689309): 319 inactive men; REHIT cycling and burpee versions each raised VO2max 8% to 13% against a non-exercising control. Metcalfe et al. (BMC Public Health, 2020; PMID 32164631): the gain held unsupervised in 25 office workers. Ruffino et al. (Applied Physiology, Nutrition, and Metabolism, 2017; PMID 28121184): 16 men with type 2 diabetes; no improvement in insulin sensitivity or glucose. Background, not REHIT: Sloth et al. (Scandinavian Journal of Medicine and Science in Sports, 2013; PMID 23889316), sprint interval training, 19 studies of which 4 were randomized; Milanović et al. (Sports Medicine, 2015; PMID 26243014), interval training in adults aged 18 to 45. Grade B on measured VO2max, an instrument-recorded function; it is not A because no abstract confirms blinded assessment.
PMID 22124524 PMID 30736402 PMID 40689309 PMID 32164631 PMID 28121184 PMID 23889316 PMID 26243014
Evidence by specific use
Cardiorespiratory fitness (measured VO2max) in inactive adults, REHIT protocol
Grade B
Metcalfe et al. (Eur J Appl Physiol, 2012; PMID 22124524), Cuddy et al. (Int J Environ Res Public Health, 2019; PMID 30736402) and Hu et al. (J Exerc Sci Fit, 2025; PMID 40689309): three independent groups. B, not A, until blinded VO2max assessment is confirmed.
PMID 22124524 PMID 30736402 PMID 40689309 PMID 32164631
Insulin sensitivity and glucose control
Grade C
Metcalfe et al. (Eur J Appl Physiol, 2012; PMID 22124524) found insulin sensitivity rose in men only; Ruffino et al. (Appl Physiol Nutr Metab, 2017; PMID 28121184) found no improvement in type 2 diabetes. Mixed: C.
PMID 22124524 PMID 28121184
Cuddy et al. (Int J Environ Res Public Health, 2019; PMID 30736402) found systolic pressure fell more with REHIT than with moderate training; Ruffino et al. (Appl Physiol Nutr Metab, 2017; PMID 28121184) found no difference from walking. Not replicated against a control: C.
PMID 30736402 PMID 28121184
Why Grade B and not Grade A
Grade B reflects moderate human evidence -- typically a single strong trial, multiple smaller trials, or surrogate endpoint data without hard clinical outcome replication. To reach Grade A, REHIT / Sprint Interval Training would require at least one additional independent randomized trial demonstrating a hard clinical endpoint or objectively measured functional outcome in a comparable population.
What this grade covers and what it does not
Grade B on measured VO2max in inactive adults doing the REHIT protocol. Randomized trials from three independent groups found it rose (Metcalfe et al., 2012; PMID 22124524; Cuddy et al., 2019; PMID 30736402; Hu et al., 2025; PMID 40689309). WHY NOT A: VO2max is an instrument-recorded function that could carry an A, but the published rule requires blinded trials, and no abstract reports that VO2max was assessed blinded. WHAT THIS GRADE DOES NOT COVER: insulin sensitivity and glucose control, and blood pressure, which are graded C on their own evidence; longevity or mortality, which no REHIT trial measured; and any particular machine or app sold for the protocol.
What would move this grade
An independent randomized trial demonstrating a hard clinical endpoint -- mortality, major adverse event, or objectively confirmed functional improvement -- in an adequately powered sample, with results independently replicated, would support Grade A.
How to track whether this is working
VO2max at baseline and every 8 weeks: this is the primary endpoint in the CAROL Bike REHIT trials. Resting heart rate monthly and fasting glucose quarterly for the metabolic benefit documented in the T2D risk trials. The protocol is two 20-second all-out sprints within an 8.5-minute session, three times per week: substituting longer moderate sprints does not replicate the REHIT stimulus.