High-intensity interval training: Evidence-Based Supplement Guide

High-intensity work is effort you can hold for only a few minutes, with heavy breathing and no conversation. Ratings of perceived exertion, such as the Borg scale, are an established way to describe how hard exercise feels (PMID 7154893). A meta-analysis of 28 controlled studies in healthy adults aged 18 to 45 found that interval training and continuous endurance training both produced large gains in VO2max (PMID 26243014). The gains were somewhat greater after interval training (PMID 26243014). In one trial, 40 moderately trained men did eight weeks of training matched for total work. Four 4-minute intervals at 90 to 95 percent of maximal heart rate, with 3 minutes of easier running between, raised VO2max more than steadier running (PMID 17414804). Hard sessions are usually a small part of training. Descriptive studies of competitive endurance athletes converge on about 80 percent of sessions at low intensity and about 20 percent dominated by high-intensity work (PMID 20861519).

1. **Build a base first.** Spend several weeks on regular easy aerobic work before adding intervals, since most training in successful athletes is easy (PMID 20861519). 2. **Pick one format.** The 4 x 4 format used four 4-minute hard efforts with 3 minutes of easier work between them (PMID 17414804). 3. **Keep hard sessions to a small share of the week.** About one in five sessions was high intensity in the athlete studies (PMID 20861519). 4. **Steer by effort as well as by numbers.** A perceived exertion scale is an established way to rate how hard a session feels (PMID 7154893).

The 4 x 4 trial ran three sessions a week for eight weeks (PMID 17414804). The meta-analysis included programmes of two weeks or longer, and longer programmes tended to give larger gains (PMID 26243014).

- **The 4 x 4 trial studied 40 moderately trained men**, so the size of the effect may differ in women, older adults and beginners (PMID 17414804). - **The meta-analysis covered healthy adults aged 18 to 45** (PMID 26243014). - **VO2max is one measure of fitness**, and these trials did not follow long-term health outcomes (PMID 26243014, 17414804). - **The 80 percent pattern describes competitive athletes** training 10 to 13 times a week (PMID 20861519). - **This guide has not been reviewed by a clinician.** `reviewStatus` above says so.

- **If you have a long-term health condition or take regular medicines, check with a clinician before starting interval training.** - **Build up gradually.** Add intervals only after weeks of regular easy training, and keep most sessions easy (PMID 20861519).

No ingredient is linked from this guide. It covers how to structure hard training, and it does not point to a product.

| PMID | Title | | --- | --- | | 7154893 | "Psychophysical bases of perceived exertion" | | 26243014 | "Effectiveness of High-Intensity Interval Training (HIT) and Continuous Endurance Training for VO2max Improvements: A Systematic Review and Meta-Analysis of Controlled Trials" | | 17414804 | "Aerobic high-intensity intervals improve VO2max more than moderate training" | | 20861519 | "What is best practice for training intensity and duration distribution in endurance athletes?" |