The Effects of Brief Supramaximal Exercise on Maximal Aerobic Capacity

Non-communicable diseases (NCDs) are the leading cause of death worldwide. Physical inactivity is a risk factor of NCDs. Although exercise recommendations have been made, many people do not meet these criteria. Lack of time is one of the main perceived exercise barrier. To address this barrier, more time-efficient exercise protocols have been developed. One of these is Reduced-Exertion High-Intensity Interval Training (REHIT), which comprises two repeated 20-s ‘all-out’ sprints with in a 10-minute protocol. Health benefits from REHIT have been demonstrated; e.g. REHIT improves V̇O2max and insulin sensitivity in healthy individuals. However, no studies have examined whether the REHIT protocol can be modified to make it either shorter or easier, without affecting the beneficial changes in V̇O2max. The effects of REHIT on V̇O2max in different participants still require investigation, and the mechanisms of the increase in V̇O2max remain unclear. Therefore, the aims of this thesis were to optimise the REHIT protocol to be a time-efficient and effective protocol for improved V̇O2max, to investigate the mechanisms underlying the improvement in V̇O2max after REHIT, and to examine the effect of REHIT on V̇O2max in type 2 diabetes (T2D) patients. Reducing the number of sprint repetitions (Chapter 2) and sprint duration (Chapter 3) attenuated the improvements in V̇O2max with REHIT, but training fewer sessions per week (Chapter 4) did not attenuate the improvements in V̇O2max. Importantly, the affective responses associated with REHIT are similar when compared with current exercise recommendations (Chapter 5). V̇O2max increases but insulin sensitivity does not change following REHIT in T2D patients (Chapter 6). Despite glycogen depletion using a protocol with single sprints, no changes in serum levels of the myokine SPARC nor V̇O2max were observed, so no information on possible mechanisms could be drawn from this thesis. Overall, it can be concluded that a manageable, effective and time-efficient exercise protocol for improving V̇O2max is REHIT, consisting of two 20-s ‘all-out’ cycle sprints within a 10-minute session performed at least two times per wee

No effect of acute and chronic supramaximal exercise on circulating levels of the myokine SPARC

Myokines may play a role in the health benefits of regular physical activity. Secreted protein acidic rich in cysteine (SPARC) is a pleiotropic myokine that has been shown to be released into the bloodstream by skeletal muscle in response to aerobic exercise. As there is evidence suggesting that SPARC release may be linked to glycogen breakdown and activation of 5’ adenosine monophosphate-activated protein kinase, we hypothesised that brief supramaximal exercise may also be associated with increased serum SPARC levels. In the present study, 10 participants (3 women; mean ± SD age: 21 ± 3 y, body mass index (BMI): 22 ± 3 kg m−2, and V˙O2max: 39 ± 6 mL kg−1 min−1) performed an acute bout of supramaximal cycle exercise (20-s Wingate sprint against 7.5% of body mass, with a 1-min warm-up and a 3-min cool-down consisting of unloaded cycling). Serum SPARC levels were determined pre-exercise as well as 0, 15, and 60 min post-exercise and corrected for plasma volume change. To determine whether regular exercise affected the acute SPARC response, participants repeated the acute exercise protocol three times per week for four weeks, and serum SPARC response to supramaximal exercise was reassessed after this period. Acute supramaximal exercise significantly decreased plasma volume (−10%;p < .001), but was not associated with a significant change in serum SPARC levels at either the pre-training or post-training testing sessions. In conclusion, in contrast to aerobic exercise, a single brief supramaximal cycle sprint is not associated with an increase in serum SPARC levels, suggesting that SPARC release is not related to skeletal muscle glycogen breakdown

Affective and perceptual responses during reduced-exertion high-intensity interval training (REHIT)

We have previously demonstrated that reduced-exertion high-intensity interval training (REHIT) is a genuinely time-efficient exercise strategy for improving cardiometabolic health. Here, we examined the affective and perceptual responses to REHIT. Eight young men and women (age 21 ± 1 y, BMI 24.9 ± 2.1 m/kg2, V̇O2max 39 ± 10 ml/kg/min) and 11 men with type 2 diabetes (T2D; age 52 ± 6 y, BMI 29.7 ± 3.1 m/kg2, V̇O2max 29 ± 5 ml/kg/min) took part in three-arm crossover trials with RPE and affective valence measured during, and enjoyment and exercise preferences measured following either: 1) REHIT (2 × 20-s sprints in a 10-min exercise session), 2) HIIT (10 × 1-min efforts) and 3) 30 min MICT. Furthermore, 19 young men and women (age 25 ± 6 y, BMI 24 ± 4 m/kg2, V̇O2max 34 ± 8 ml/kg/min) completed a 6-week REHIT intervention with affective valence during an acute REHIT session measured before and after training. Affect decreases (briefly) during REHIT, but recovers rapidly, and the decline is not significantly different when compared to MICT or HIIT in either healthy participants or T2D patients. Young sedentary participants reported similar levels of enjoyment for REHIT, MICT and HIIT, but 7 out of 8 had a preference for REHIT. Conversely, T2D patients tended to report lower levels of enjoyment with REHIT compared with MICT. The decrease in affective valence observed during an acute REHIT session was significantly attenuated following training. We conclude that affective and perceptual responses to REHIT are no more negative compared to those associated with MICT or HIIT, refuting claims that supramaximal sprint interval training protocols are associated with inherent negative responses

A comparison of the health benefits of reduced-exertion high-intensity interval training (REHIT) and moderate-intensity walking in type 2 diabetes patients

Reduced-exertion high-intensity interval training (REHIT) is a genuinely time-efficient intervention that can improve aerobic capacity and insulin sensitivity in sedentary individuals. The present study compared the effects of REHIT and moderate-intensity walking on health markers in patients with type 2 diabetes (T2D) in a counter-balanced crossover study. Sixteen men with T2D (mean ± SD age: 55 ± 5 years, body mass index: 30.6 ± 2.8 kg·m−2, maximal aerobic capacity: 27 ± 4 mL·kg−1·min−1) completed 8 weeks of REHIT (three 10-min low-intensity cycling sessions/week with two “all-out” 10–20-s sprints) and 8 weeks of moderate-intensity walking (five 30-min sessions/week at an intensity corresponding to 40%–55% of heart-rate reserve), with a 2-month wash-out period between interventions. Before and after each intervention, participants underwent an incremental fitness test, an oral glucose tolerance test (OGTT), a whole-body dual-energy X-ray absorptiometry scan, and continuous glucose monitoring. REHIT was associated with a significantly larger increase in maximal aerobic capacity compared with walking (7% vs. 1%; time × intervention interaction effect:p< 0.05). Both REHIT and walking decreased resting mean arterial pressure (−4%; main effect of time:p< 0.05) and plasma fructosamine (−5%; main effect of time:p< 0.05). Neither intervention significantly improved OGTT-derived measures of insulin sensitivity, glycaemic control measured using continuous glucose monitors, blood lipid profile, or body composition. We conclude that REHIT is superior to a 5-fold larger volume of moderate-intensity walking in improving aerobic fitness, but similar to walking REHIT is not an effective intervention for improving insulin sensitivity or glycaemic control in T2D patients in the short term

Decreasing sprint duration from 20 to 10 s during reduced-exertion high-intensity interval training (REHIT) attenuates the increase in maximal aerobic capacity but has no effect on affective and perceptual responses

Purpose: Recent studies have demonstrated that modifying the ‘classic’ 6x30-s ‘all-out’ sprint interval training (SIT) protocol by incorporating either shorter sprints (6x10-s or 15-s sprints) or fewer sprints (e.g. 2x20-s sprints; reduced-exertion high-intensity interval training (REHIT)) does not attenuate the training-induced improvements in maximal aerobic capacity (V̇O2max). The aim of the present study was to determine whether reducing the sprint duration in the REHIT protocol from 20 s to 10 s per sprint influences acute affective responses and the change in V̇O2max following training. Methods: Thirty-six sedentary or recreationally active participants (17 women; mean±SD age: 22±3 y, BMI: 24.5±4.6 kg·m-2, V̇O2max: 37±8 mL·kg-1·min-1) were randomised to a group performing a ‘standard’ REHIT protocol involving 2x20-s sprints or a group who performed 2x10-s sprints. V̇O2max was determined before and after 6 weeks of 3 weekly training sessions. Acute affective responses and perceived exertion were assessed during training. Results: Greater increases in V̇O2max were observed for the group performing 20-s sprints (2.77±0.75 to 3.04±0.75 L·min-1; +10%) compared to the group performing 10-s sprints (2.58±0.57 vs. 2.67±3.04 L·min-1; +4%; group×time interaction effect: p<0.05; d=1.06). Positive affect and the mood state vigour increased post-exercise, while tension, depression and total mood disturbance decreased, and negative affect remained unchanged. Affective responses and perceived exertion were not altered by training and were not different between groups. Conclusion: Reducing sprint duration in the REHIT protocol from 20 s to 10 s attenuates improvements in V̇O2max, and does not result in more positive affective responses or lower perceived exertion