Reduced-Exertion, High-Intensity Interval Training: The Effects of a Shortened-Sprint Protocol on Affective Response and V̇O2max, with Perspective on Application to HbA1c Defined Non-Diabetic Hyperglycaemia

Background

Physical inactivity is an endemic health problem. Despite evidence to suggest regular physical activity and exercise improve health, the challenge of encouraging individuals and populations to be more active remains. Frequently, ‘lack of time’ is cited as the main barrier. Proponents of high-intensity interval training (HIT) emphasise time-efficiency as a practical benefit and contend that the health outcomes associated with this type of exercise are relevant to public health strategy. This includes increased cardiovascular fitness and improved blood glucose control. However, many iterations of HIT are not appreciably more time-efficient than traditional exercise guidelines, and the high-intensity nature of HIT may result in negative affective states (increasing displeasure) that could lead to poor exercise adherence. Reduced-exertion HIT (REHIT) has been developed as a genuinely time-efficient and more tolerable approach to exercise.

Aims

The principal aims of the thesis focus on two related areas of exercise science: approaches to time-efficient exercise to improve health outcomes; and the affective response to such exercise. The contribution to knowledge is predicated on critical appraisal of current literature, and based on data collected via three studies distinct in their focus and application, but connected by the theme of exploring a novel approach to REHIT that, despite including maximal capacity exercise, does not overly compromise affective response.

Methods

Study 1 used a randomised crossover design to consider differences between responses to three low-volume, high-intensity exercise protocols. Shortened-sprint REHIT (8 × 5 s sprints) was compared to traditional REHIT (2 × 20 s sprints) and sprint continuous training (SCT, one sustained maximal effort sprint). The primary outcome measure was affect (pleasure-displeasure) measured using the Feeling Scale (FS). Study 2 used a randomised controlled design to compare the effects of shortened-sprint and traditional REHIT on peak oxygen uptake (V̇O2peak), to determine if shorter sprints attenuate increases in this important health outcome. Finally, study 3 was a feasibility study to report data relevant to the acceptability of a REHIT intervention with non-diabetic hyperglycaemia (NDH) patients delivered in a National Health Service (NHS) practice setting.

Results

For study 1, peak affective valence was more positive for shortened-sprint REHIT (1.4 ± 1.7 FS units) compared to traditional REHIT (-0.1 ± 1.9) and SCT (-0.8 ± 1.6), where 1 is ‘fairly good’, 0 is ‘neutral’, and -1 is ‘fairly bad’ (both p = 0.001). Greater pleasure was also observed for traditional REHIT compared to SCT (p = 0.005). Likewise, lower ratings of perceived exertion (RPE) and higher enjoyment were associated with shortened-sprint REHIT (all p < 0.01). Both iterations of REHIT avoided large negative peaks in affective response and may therefore be genuinely time-efficient, yet tolerable approaches to exercise. Shorter sprints may be additionally beneficial in circumventing negative affective responses. In study 2, compared to baseline, V̇O2peak increased following both conditions (6% for shortened-sprint REHIT [d = -0.36] and 9% for traditional REHIT [d = -0.53], both p = 0.01). However, there was substantial heterogeneity in training response within each condition (range -2% to 20%). Affective valence was again more favourable for shortened-sprint REHIT compared to traditional REHIT (1.6 ± 0.6 vs 0.2 ± 1 FS units, respectively, p = 0.001, d = 1.62). Similarly, peak RPE values were lower for shortened-sprint REHIT (14.4 ± 0.9 vs 16.2 ± 1.1, p = 0.001, d = -1.71). Despite this, there was no significant difference in enjoyment between the two protocols. For study 3 (feasibility study), the findings of this preparatory stage of trial design pre-empted problems with the intervention that could be changed to optimise the design and conduct of a larger-scale pragmatic trial to improve transferability into real-world practice. Challenges included eligibility, recruitment, patient consent, and poor clinician engagement leading to the recommendation that the study was not feasible in its current form. These findings form the basis for important learning in relation to the potential for transfer of exercise interventions into real-life scenarios with specific populations. Future interventions need to be sensitive to features of the local context such as the built environment, socioeconomic status, and the specific needs of individuals with chronic disease.

Conclusion

The original contribution to knowledge in this thesis is that a novel REHIT protocol using shortened-sprints can improve V̇O2peak whilst minimising large negative peaks in affective response. Thus, the three studies provide preliminary evidence to suggest that REHIT is both time-efficient, yet at the same time does not overly compromise affective response. Although there is no claim to invalidate the efficacy of higher volume exercise, the practicalities of building REHIT into everyday life could improve exercise adherence. Translating current evidence into effective exercise strategies in real-world settings remains a key challenge to further research on REHIT. To counter the deleterious effects on health that modern environments create, we need to engineer physical activity into our lives in a way that is socially and culturally acceptable. REHIT could form part of a solution to achieve this.