Introduction and Purpose SPRINT AND HIGH-INTENSITY INTERVAL TRAINING AND THEIR INFLUENCE ON RESTING METABOLIC RATE AND SUBSTRATE OXIDATION Rebekah F. Seay, CSCS, EP-C, Holly E. Clarke, CSCS, EP-C, Katie K. Spain, and Matthew M. Schubert, PhD, CISSN, EP-C. Department of Kinesiology, Auburn University at Montgomery, Montgomery, AL Abstract PURPOSE: Resting metabolic rate (RMR) and substrate oxidation have been linked with a number of health outcomes. Resistance training may increase metabolic rate while endurance training may help maintain metabolic rate with weight loss. However, the effects of high-intensity training on metabolic rate have not been closely examined. Therefore, the purpose of this investigation was to compare the effects of sprint and high-intensity training on RMR and substrate oxidation. METHODS: 22 (to date) men and women were assigned to either a sprint-interval training (SIT, n=8), high-intensity interval training (HIT, n=8), or a control condition (CON, n=6). Before and after 4 weeks of training, participants completed assessments for body composition, RMR, VO2max, energy intake, and physical activity. RESULTS: RMR and RQ did not statistically change in any of the groups. However, 67% of the participants in the experimental groups exhibited a change in RMR greater than 2x(TE), suggesting a meaningful change. Body mass did not change, though FM decrease by ~0.5 kg whilst FFM increased by ~0.5 kg in the experimental groups. VO2max did not significantly differ between groups, though HIT (+6.1%) and SIT (+11.6%) were greater after the intervention. CONCLUSIONS: Four weeks of interval training caused statistically non-significant but clinically meaningful changes in a number of variables. Studies with larger samples are needed to confirm these results. Results Table 2: Changes in Body Composition, Diet, and Activity (Means ± Standard Deviation) Figure: Top panels, pre/post changes in fasting RMR and RQ (Means ± Standard Deviation with individual participants Bottom panels, change scores in fasting RMR and RQ for individuals; dashed lines represent 2x typical error of measurement (“true” response outside of technical/biological variation) CONTROL HIT SIT Body Mass (kg) Pre 82.8 ± 19.1 76.2 ± 16.2 76.0 ± 9.6 Body Mass (kg) Post 83.1 ± 18.9 75.7 ± 16.3 76.1 ± 9.5 Body Fat (%) Pre 20.8 ± 7.8 23.1 ± 9.0 25.0 ± 9.1 Body Fat (%) Post 21.0 ± 8.0 22.5 ± .2 23.8 ± 8.3 Fat Mass (kg) Pre 17.6 ± 9.6 17.8 ± 8.5 19.3 ± 8.5 Fat Mass (kg) Post 17.9 ± 9.8 17.3 ± 8.9 18.5 ± 7.9 Fat-free Mass (kg) Pre 65.2 ± 14.2 58.1 ± 13.4 56.6 ± 7.2 Fat-free Mass (kg) Post 65.2 ± 14.0 58.3 ± 13.2 57.5 ± 6.2 Waist Circumference (cm) Pre 79.0 ± 7.4 79.3 ± 7.8 81.8 ± 7.2 Waist Circumference (cm) Post 79.5 ± 7.0 79.1 ± 7.3 80.7 ± 7.2 Energy Intake (kcal) Pre 2584 ± 638 2360 ± 542 2350 ± 355 Energy Intake (kcal) Post 2544 ± 658 2391 ± 516 2359 ± 365 Sedentary time (%) Pre 61.9 ± 6.6 58.9 ± 7.8 62.6 ± 11.1 Sedentary time (%) Post 63.3 ± 5.9 57.5 ± 9.4 60.6 ± 10.6 Light PA (%) Pre 21.6 ± 2.5 25.3 ± 5.6 23.7 ± 6.7 Light PA (%) Post 20.9 ± 1.5 26.0 ± 5.6 25.4 ± 6.3 MVPA (%) Pre 16.5 ± 4.6 15.8 ± 3.5 13.7 ± 5.3 MVPA (%) Post 15.8 ± 4.6 14.0 ± 5.4 Steps per day Pre 12,378 ± 3,572 11,431 ± 3,023 9,498 ± 3,348 Steps per day Post 12,167 ± 3,773 12,307 ± 4,178 9,456 ± 2,825 Introduction and Purpose Low volume, high-intensity interval training (HIT) has been promoted as a more time-efficient and similar or more potent stimulus than continuous moderate-intensity training (Gillen et al., 2016; Burgomaster et al., 2008; Gibala et al., 2012). HIT, and one of its relatives’ sprint-interval training (SIT, defined as “supramaximal” or Wingate-based training, (Weston et al., 2014)), have been shown to influence a number of health outcomes, including: cardiorespiratory fitness and maximal fat oxidation (Astorino et al., 2013a; Astorino et al., 2013b; Gist et al., 2014), changes in skeletal muscle proteins and markers of mitochondrial function (Gillen et al., 2013; Gurd et al., 2010; Little et al., 2010), reduced insulin resistance (Earnest et al., 2013; Little et al., 2011), and body composition (Gillen et al., 2013). Despite all of these positive benefits, relative little attention has been given to the influence of interval training on resting metabolic rate and fasting substrate oxidation (Whyte et al., 2010; Sevits et al., 2013; Fisher et al., 2015; Martins et al., 2016). A low RMR has been linked with weight gain over time in some studies (Luke et al., 2006) but not others (Anthanont and Jensen, 2016; Shook et al., 2015), and Shook et al. reported that individuals with higher fasting respiratory quotients (RQ, a proxy of fasting substrate oxidation), indicative of a greater portion of carbohydrates being oxidized, gained larger amounts of weight than individuals with lower RQs (Shook et al., 2015). Thus, the purpose of this study was to examine the influence of 4 weeks of SIT and HIT training on fasting RMR and RQ in healthy men and women. Discussion Primary findings: -Statistically non-significant changes in RMR occurred in the two training groups -HIT increased +2.5% and SIT by +3% -5/8 participants in each group exhibited changes (increases) in RMR that were greater than 2x TE, indicative of a true response (Bonafiglia et al. 2016; Hopkins 2000) -Statistically non-significant increases were also observed in VO2max and fasting percent macronutrient oxidation: -SIT: +11.6% VO2max, -13.8% CHOOX, and + 7% FATOX -HIT: +6.1% VO2max, -10.1% CHOOX, and + 4% FATOX Acutely, IT has been reported to cause transient increases in RMR and decreases in RQ (Sevits et al. 2013; Kelley et al. 2013; Whyte et al. 2010). Importantly, these transient changes appear to dissipate within 48 hours, making the timing of assessment critical to ensure the most valid data are collected. Therefore, our window was ~72 hours after the participants’ last training session in order to minimize any transient effects of the IT bouts on RMR and RQ. The handful of training studies to assess RMR in response to IT have generally reported no significant changes (Fisher et al. 2015; Martins et al. 2016). Data from the MET-1 exercise trial reported significantly increased RMR in women and men after a 16 month intervention (Potteiger et al. 2008). In contrast, the later MET-2 study reported no significant changes in RMR after 10 months of supervised aerobic exercise, despite substantial weight loss (Willis et al. 2014). We acknowledge our limited sample (n=22) decreased our ability to detect significant differences between groups; we anticipate a total sample of 30-32 by conclusion of data collection. Contact: mschuber@aum.edu Methods Table 1: Changes in Fitness and Exercise Metabolism (Means ± Standard Deviation) Healthy men and women were randomized to either a sprint interval training group or a high-intensity interval training group. Individuals who did not wish to complete the training but were interested in the results of testing self-selected into the control group. Individuals trained 3 days per week for four weeks. Heart rate, RPE, affect (Feeling Scale), and pain were assessed before and after each interval (within ~5 seconds). The SIT group completed a modification of that previously described by Gillen et al. (PloS ONE 2016), consisting of 2 minute warm-up @ 10% Peak Power Output (PPO), 3x 20-second sprints at a resistance equivalent to 5% baseline body weight with 2 minute recoveries @ 10% PPO, and 3 minute cool down @ 10% PPO. Week 2 increased to 4 sprints and weeks 3 & 4 incorporated 5 sprints. Total time per training session ranged from 10 minutes during week 1 to ~15 minutes during week 4. The HIT group completed 1 minute intervals @ 90% PPO with 1 minute recoveries @ 10% PPO with an equivalent warm-up and cool-down to the SIT group. 6 bouts were performed during weeks 1 & 2 and 8 during weeks 3 & 4. Total time per training session ranged from 16 minutes in week 1 to 20 minutes in week 4. Before and after all training, subjects underwent tests for resting metabolic rate and substrate oxidation, maximal aerobic capacity and fat oxidation, body composition, a 3 day food record, and 7 days of wrist-worn accelerometry. Data were analyzed in SPSS using repeated-measures ANOVA. To assess individual responses, the “true” response was determined from two times the typical error of measurement (Bonafiglia et al. PLoS ONE 2016) CONTROL (n=6) HIT (n=8) SIT (n=8) VO2max (mL∙kg-1∙min-1) Pre 37.5 ± 8.3 33.9 ± 10.1 36.0 ± 6.5 VO2max (mL∙kg-1∙min-1) Post 37.0 ± 8.8 36.1 ± 10.7 40.6 ± 8.9 Peak Power Output (W) Pre 235 ± 93 210 ± 66 225 ± 43 Peak Power Output (W) Post 238 ± 90 233 ± 61 248 ± 36 Maximal Rate of Fat Oxidation (g∙min-1) Pre 0.28 ± 0.13 0.24 ± 0.11 0.22 ± 0.08 Maximal Rate of Fat Oxidation (g∙min-1) Post 0.25 ± 0.14 0.25 ± 0.10 0.24 ± 0.12 Maximal Rate of Fat Oxidation (% of VO2max) Pre 42.5 ± 7.1 48.5 ± 9.0 39.6 ± 4.4 Maximal Rate of Fat Oxidation (% of VO2max) Post 41.0 ± 7.6 44.0 ± 7.4 36.2 ± 7.1