High intensity interval training: moving away from the laboratory and into the real-world

Abstract

Within the laboratory setting, high intensity interval training (HIIT) can elicit physiological adaptations similar to traditional moderate intensity continuous training (MICT) with the important advantage of a reduced total exercise volume and time commitment. However, researchers have argued that HIIT is not a viable public health strategy because it is too demanding to be maintained by non-athletic populations (Biddle and Batterham, 2015). The aim of this thesis was to investigate the effect of real-world HIIT interventions on adherence and cardio-metabolic health risk factors. Furthermore this thesis investigates the feasibility and perceptual responses to home-based wholebody HIIT as a strategy to remove many of the major barriers to exercise. In Chapter 3, 82 previously sedentary males (n=26) and females (n=56) aged 18-65 (28±10 y, BMI 25±3 kg.m-2) participated in the study. In a randomised cross-over design, whereby participants completed either 6 weeks of 30HIT (4-8x30s sprint with 120s active recovery) and 6-weeks of 60HIT (6-10x60s sprint with 60s active recovery). Participants then completed a 4-week washout period before completing the alternative intervention. Training sessions were completed on a Wattbike, 3 times per week. VO2peak, body composition (DXA), glycaemic control (oral glucose tolerance test (OGTT) and arterial stiffness (aortic pulse wave velocity (aPWV)) were assessed pre and post each 6-week training phase. VO2peak increased post intervention in 30HIT and 60HIT (P 0.05). In Chapter 4, 154 patients (males: n=88), females: n=66) who were eligible for a UK exercise referral scheme (ERS) (inactive and at least one health risk factor) were recruited. Participants chose either 12-weeks ERS (encouraged to achieve 150min/wk of moderate-intensity exercise, with reduced cost gym membership) or Home-based HIIT (4-9x1min intervals interspersed with 1 min rest, using body weight exercises). Adherence and compliance to the programme were monitored using a heart rate monitor. VO2peak, body composition (DXA), glycaemic control (OGTT) and arterial stiffness (aPWV) was recorded at baseline, post-intervention (12-weeks) and 3-months postintervention (follow-up). Perceptions of the programme were evaluated using an online interview. 56% (n=87) of eligible participants chose Home-based HIIT in preference to ERS. At baseline Home-based HIIT had a lower VO2peak than ERS (P=0.034). ERS and Home-based HIIT had a similar adherence (HIIT 39%, ERS 53% P=0.298) and compliance to the prescribed programme (HIIT 30%, ERS 47% P=0.331). VO2peak increased post-intervention (P<0.001) in both groups and this was maintained at follow-up (P=0.287). The interview revealed Home-based HIIT was positively received, and the convenience of the programme reduced some of the perceived barriers to exercise. Finally, in Chapter 5, 27 recreationally active (≥1 hr exercise/wk) participants (male/female: n=13/14, age: 223y, BMI: 24.32.4, VO2peak: 42.27.2 ml.min1.kg-1) completed a randomised counter-balanced cross over design. To assess the acute physiological (heart rate and lactate) and perceptual responses (feeling scale, felt arousal scale and rate of perceived exertion) to four different HIIT protocols (Ergo-60:60: cycling 10x60s at 100%Wmax with 60s rest, BW-60:60: whole-body exercise 10x60s with 60s rest, SM-20:10:following a social media video 20x20s with 10s rest, SM-40:20: following a social media video 15x40s with 20s rest). BW-60:60 resulted in significantly higher interval heart rate peak (P<0.001) compared to all other protocols, and a significantly higher change in lactate compared to SM-20:10 (P<0.001). No differences were observed between groups when reporting lowest recorded feeling scale (P=0.292), but differences in the feeling scale profile during exercise did exist between the protocols used within the research (Ergo-60:60 & BW-60:60) and the social media protocols. Greater post-session enjoyment was reported in BW-60:60 compared to Ergo-60:60 (P=0.004) despite using the same work:rest ratio. In conclusion, this thesis provides strong evidence that sedentary or at risk participants are able to complete HIIT at the correct prescribed intensity to induce health benefits in a free-living environment. Furthermore, Home-based HIIT was an attractive option for at-risk patients referred to an ERS, and had similar adherence to the traditional exercise prescription guidelines. Additionally, body-weight HIIT and social media videos are promising enjoyable options, compared to traditional cycling-based HIIT. Therefore we provide strong evidence that the prescription of HIIT, especially a Home-based HIIT programme using body-weight exercises, is both effective and feasible for a non-athletic population in the real world.