Mostly easy, sometimes brutal: polarised training won the time trials

Endurance athletes have a fixed number of hours a week, so the biggest question in training design is how those hours are distributed across intensities. Two models compete for the answer. Polarised training puts the bulk of the work at easy intensities and reserves a small portion for very hard efforts. Threshold training concentrates more of the load in the middle, around the lactate threshold. Descriptions of what elite athletes happen to do cannot settle the argument, because the fastest athletes may simply train more or have trained longer, so randomised comparisons are needed.

The reviewers searched SPORTDiscus, CINAHL Complete and Medline, with the search run on November 6, 2016, and registered the protocol in advance. To be eligible, a study had to allocate athletes at random, recruit endurance-trained athletes with greater than 2 years of training experience and a VO2max or VO2peak above 50 ml per kg per min, include both a polarised and a threshold group, and measure either internal outcomes such as VO2max or external outcomes such as a time trial. The databases returned a combined 329 results. Four studies met the criteria for the written review and 3 provided data for pooling. Methodological quality was rated on the PEDro scale.

Time-trial performance was the only outcome with enough data to combine, and the pooled result showed a moderate effect favouring the polarised groups over the threshold groups. Across the wider set of four studies, 3 reported time-trial performance, 3 reported VO2max or VO2peak, 2 measured time to exhaustion and one assessed exercise economy. Quality ratings were middling: two studies scored 4/10 on the PEDro scale and two scored 5/10. The authors phrase the conclusion carefully, saying polarised training may lead to greater improvement rather than that it does.

This supports the popular case for polarised training with actual randomised evidence rather than descriptive accounts of elite practice, but it does so on a very small base. With only four qualifying trials and modest quality scores, the size of any real advantage is uncertain, and there was not enough data to pool the physiological outcomes such as VO2max, time to exhaustion or exercise economy. It also leaves untouched the question of whether the benefit comes from the very hard sessions, the easy volume, or simply from a change in stimulus.

For a trained endurance athlete, this is a reason to take the polarised approach seriously rather than assuming that more time near threshold means more fitness. It is not strong enough to justify treating threshold work as a mistake, since the comparison rests on three pooled trials of moderate quality. The athletes studied were already well trained with high aerobic capacity, so it says nothing reliable about beginners or recreational exercisers building base fitness. Treat it as a plausible direction rather than a settled rule.