For decades, the gospel of endurance training has been built on a small library of intervention studies, most lasting eight to twelve weeks and most run on healthy young men. A scoping review published this winter in the Journal of Functional Morphology and Kinesiology now puts a number on the imbalance: of 617 studies of aerobic training and VO2max gathered for analysis, 363 — almost three in every five — used moderate intensity continuous training, while interval-based protocols and durations longer than three months were systematically under-represented. For amateur runners trying to navigate the latest intervals fad, that is a useful reality check.
The review's headline figure for protocol design is plain. When training intensity was distilled across the 617 studies, the largest, most reliable VO2max gains came not from the trendy long-tempo work but from short, sharp efforts above lactate threshold. A network meta-analysis published earlier in the spring, using a subset of 38 controlled trials, found that repeated sprint training (RST), high-intensity interval training (HIIT) and sprint interval training (SIT) all produced bigger improvements in VO2max than continuous running, with RST showing the largest effect size. The most consistent gains were observed when athletes ran 140-second efforts with 165 seconds of recovery, three times a week, for between three and six weeks.
The catch, the reviewers argue, is everything that those studies do not tell us. Female participation across the 617 studies sat well below 30 per cent, the median intervention lasted 11.4 weeks, and only a handful of trials reported menstrual cycle phase or hormonal contraceptive use. Long-term studies of more than 12 weeks were rare, and almost none compared protocols head-to-head over six months. That matters because amateur runners do not train for six weeks at a time; they train for a marathon block of 16 to 20 weeks and then return to base before the next cycle. The review also flagged inconsistent reporting of participants' starting fitness, which tends to inflate apparent gains.
Read carefully, the review is more a guidance document for coaches than a permission slip to bin steady miles. Continuous running still produced reliable VO2max gains across the studies — just smaller ones than well-designed intervals. And the review's authors are explicit that the work tested in trials is rarely representative of the whole training week of a club runner: a typical 50-mile-per-week amateur is doing perhaps 20 per cent intervals and 80 per cent continuous running, a ratio almost no published study replicates. The take-home is therefore not "drop the easy runs", but "be honest about which sessions are actually moving your ceiling, and which are maintaining it".
For practical training in May, the studies suggest a small set of practical changes. First, treat one weekly session as your VO2max-pushing workout — short reps, near-max effort, with rest long enough to repeat the quality. Second, do not add a second VO2max session without dropping a different intensity day; the review's strongest gains came from three quality sessions per week sitting on a base of low-intensity work. Third, give the block at least six weeks before judging whether it has worked. The review's biggest practical message — and the one most often missed — is that VO2max is trainable but slow; expecting weekly progress is a route to overtraining and to the sort of incomplete intervention that already crowds the literature.