Rebuttal from Tanya M. Holloway and Lawrence L. Spriet

Wisløff et al. (2015) present epidemiological studies that demonstrate evidence for risk reduction as a result of high intensity interval training (HIIT). However, it is undeniable that many important health problems affecting modern society are due to the markedly different physical activity (PA) patterns from those to which humans were genetically adapted (Booth et al. 2008). When our current genome was originally selected, daily PA was obligatory and our biochemistry and physiology functioned optimally in such circumstances. Beginning with primitive civilizations, in which large amounts of energy expenditure were required to survive in the natural environment (25,000 years ago; ∼1240 kcal day⁻¹), human energy expenditure has progressively declined (modern day ∼555 kcal day⁻¹) (Eaton et al. 1988; Cordain et al. 1998) and lifestyle‐related disease rates (e.g., diabetes mellitus, ischemic heart disease) have skyrocketed since the second industrial revolution.

While there is evidence to support the use of HIIT, the evidence identifying detrimental effects of HIIT cannot be overlooked (Middleton et al. 2006; Scott et al. 2010), and may actually be more prevalent than previously reported (Levinger et al. 2015). Such negative evidence does not exist for moderate intensity PA. Natural selection shaped the human genome not to perform any particular form of activity exclusively, and we propose the graded addition of HIIT, where clinically appropriate, to daily moderate PA (e.g. 2–3 days of HIIT interspersed with days of moderate continuous training). This has been suggested to most closely mimic the activity patterns of our genetic ancestors (O'Keefe et al. 2011). Let us also not forget the important inclusion of other activities for overall health benefit, e.g. resistance training (Leenders et al. 2013). Ultimately, the significant literature on the benefits of moderate PA cannot be discounted, and HIIT should not be utilized in isolation, as the evidence for this remains limited compared to moderate daily PA.

While we agree that a ‘lack of time’ remains the prominent reason for inadequate participation in PA, in our opinion it would be premature to suggest that 1 day per week of any form of exercise, HIIT or otherwise, is sufficient for optimal health. Ultimately, to reduce current PA recommendations in order to make it more attainable for those not meeting the guidelines is akin to suggesting partial smoking cessation, which would have enormous consequences on health compared to targeted total cessation (Morris et al. 2015). Also, to our knowledge, no evidence exists to suggest that a single bout of exercise is equivalent to the health benefits observed when meeting the current guidelines for daily PA. Let us not disregard what we have known for centuries: ‘Lack of activity destroys the good condition of every human being, while movement and methodical physical exercise save and preserve it’ (Plato 350 BC).

Call for comments

Readers are invited to give their views on this and the accompanying CrossTalk articles in this issue by submitting a brief (250 word) comment. Comments may be submitted up to 6 weeks after publication of the article, at which point the discussion will close and the CrossTalk authors will be invited to submit a ‘Last Word’. Please email your comment to jphysiol@physoc.org.