Mary E. Jung

Where does HIT fit? An examination of the affective response to high-intensity intervals in comparison to continuous moderate- and continuous vigorous-intensity exercise in the exercise intensity-affect continuum.

Affect experienced during an exercise session is purported to predict future exercise behaviour. Compared to continuous moderate-intensity exercise (CMI), the affective response to continuous vigorous-intensity exercise (CVI) has consistently been shown to be more aversive. The affective response, and overall tolerability to high-intensity interval training (HIT), is less studied. To date, there has yet to be a comparison between HIT, CVI, and CMI. The purpose of this study was to compare the tolerability and affective responses during HIT to CVI and CMI. This study utilized a repeated measures, randomized, counter-balanced design. Forty-four participants visited the laboratory on four occasions. Baseline fitness testing was conducted to establish peak power output in Watts (Wpeak). Three subsequent visits involved a single bout of a) HIT, corresponding to 1-minute at ∼100% Wpeak and 1-minute at ∼20% Wpeak for 20 minutes, b) CMI, corresponding to ∼40% Wpeak for 40 minutes, and c) CVI, corresponding to ∼80% Wpeak for 20 minutes. The order of the sessions was randomized. Affective responses were measured before, during and after each session. Task self-efficacy, intentions, enjoyment and preference were measured after sessions. Participants reported greater enjoyment of HIT as compared to CMI and CVI, with over 50% of participants reporting a preference to engage in HIT as opposed to either CMI or CVI. HIT was considered more pleasurable than CVI after exercise, but less pleasurable than CMI at these times. Despite this participants reported being just as confident to engage in HIT as they were CMI, but less confident to engage in CVI. This study highlights the utility of HIT in inactive individuals, and suggests that it may be a viable alternative to traditionally prescribed continuous modalities of exercise for promoting self-efficacy and enjoyment of exercise.

Effects of high-intensity interval exercise versus continuous moderate-intensity exercise on postprandial glycemic control assessed by continuous glucose monitoring in obese adults

The purpose of this study was to examine the impact of acute high-intensity interval training (HIIT) compared with continuous moderate-intensity (CMI) exercise on postprandial hyperglycemia in overweight or obese adults. Ten inactive, overweight or obese adults (41 ± 11 yrs, BMI = 36 ± 7 kg/m(2)) performed an acute bout of HIIT (10 × 1 min at approximately 90% peak heart rate (HRpeak) with 1-min recovery periods) or matched work CMI (30 min at approximately 65% HRpeak) in a randomized, counterbalanced fashion. Exercise was performed 2 h after breakfast, and glucose control was assessed by continuous glucose monitoring under standardized dietary conditions over 24 h. Postprandial glucose (PPG) responses to lunch, dinner, and the following days breakfast were analyzed and compared with a no-exercise control day. Exercise did not affect the PPG responses to lunch, but performing both HIIT and CMI in the morning significantly reduced the PPG incremental area under the curve (AUC) following dinner when compared with control (HIIT = 110 ± 35, CMI = 125 ± 34, control = 162 ± 46 mmol/L × 2 h, p < 0.05). The PPG AUC (HIIT = 125 ± 53, CMI = 186 ± 55, control = 194 ± 96 mmol/L × 2 h) and the PPG spike (HIIT = Δ2.1 ± 0.9, CMI = Δ3.0 ± 0.9, control = Δ3.0 ± 1.5 mmol/l) following breakfast on the following day were significantly lower following HIIT compared with both CMI and control (p < 0.05). Absolute AUC and absolute glucose spikes were not different between HIIT, CMI, or control for any meal (p > 0.05 for all). We conclude that a single session of HIIT has greater and more lasting effects on reducing incremental PPG when compared with CMI.

Affective and Enjoyment Responses to High-Intensity Interval Training in Overweight-to-Obese and Insufficiently Active Adults

High-intensity interval training (HIIT) has many known physiological benefits, but research investigating the psychological aspects of this training is limited. The purpose of the current study is to investigate the affective and enjoyment responses to continuous and high-intensity interval exercise sessions. Twenty overweight-to-obese, insufficiently active adults completed four counterbalanced trials: a 20-min trial of heavy continuous exercise and three 24-min HIIT trials that used 30-s, 60-s, and 120-s intervals. Affect declined during all trials (p < .05), but affect at the completion of trials was more positive in the shorter interval trials (p < .05). Enjoyment declined in the 120-s interval and heavy continuous conditions only (p < .05). Postexercise enjoyment was higher in the 60-s trial than in the 120-s trial and heavy continuous condition (p < .05). Findings suggest that pleasure and enjoyment are higher during shorter interval trials than during a longer interval or heavy continuous exercise.

High-Intensity Interval Training as an Efficacious Alternative to Moderate-Intensity Continuous Training for Adults with Prediabetes

Aims. High-intensity interval training (HIIT) leads to improvements in various markers of cardiometabolic health but adherence to HIIT following a supervised laboratory intervention has yet to be tested. We compared self-report and objective measures of physical activity after one month of independent exercise in individuals with prediabetes who were randomized to HIIT (n = 15) or traditional moderate-intensity continuous training (MICT, n = 17). Method. After completing 10 sessions of supervised training participants were asked to perform HIIT or MICT three times per week for four weeks. Results. Individuals in HIIT (89 ± 11%) adhered to their prescribed protocol to a greater extent than individuals in MICT (71 ± 31%) as determined by training logs completed over one-month follow-up (P = 0.05, Cohens d = 0.75). Minutes spent in vigorous physical activity per week measured by accelerometer were higher in HIIT (24 ± 18) as compared to MICT (11 ± 10) at one-month follow-up (P = 0.049, Cohens d = 0.92). Cardiorespiratory fitness and systolic blood pressure assessed at one-month follow-up were equally improved (Ps < 0.05). Conclusions. This study provides preliminary evidence that individuals with prediabetes can adhere to HIIT over the short-term and do so at a level that is greater than MICT.

Reducing the Intensity and Volume of Interval Training Diminishes Cardiovascular Adaptation but Not Mitochondrial Biogenesis in Overweight/Obese Men

Objective The purpose of this research was to determine if the adaptations to high intensity interval training (HIT) are mitigated when both intensity and training volume (i.e. exercise energy expenditure) are reduced. Methods 19 overweight/obese, sedentary males (Age: 22.7±3.9 yrs, Body Mass Index: 31.4±2.6 kg/m2, Waist Circumference: 106.5±6.6 cm) performed 9 sessions of interval training using a 1-min on, 1-min off protocol on a cycle ergometer over three weeks at either 70% (LO) or 100% (HI) peak work rate. Results Cytochrome oxidase I protein content, cytochrome oxidase IV protein content, and citrate synthase maximal activity all demonstrated similar increases between groups with a significant effect of training for each. β-hydroxyacyl-CoA dehydrogenase maximal activity tended to increase with training but did not reach statistical significance (p = 0.07). Peroxisome proliferator-activated receptor gamma coactivator-1α and silent mating type information regulator 2 homolog 1 protein contents also increased significantly (p = 0.047), while AMP-activated protein kinase protein content decreased following the intervention (p = 0.019). VO2peak increased by 11.0±7.4% and 27.7±4.4% in the LO and HI groups respectively with significant effects of both training (p<0.001) and interaction (p = 0.027). Exercise performance improved by 8.6±7.6% in the LO group and 14.1±4.3% in the HI group with a significant effect of training and a significant difference in the improvement between groups. There were no differences in perceived enjoyment or self-efficacy between groups despite significantly lower affect scores during training in the HI group. Conclusions While improvements in aerobic capacity and exercise performance were different between groups, changes in oxidative capacity were similar despite reductions in both training intensity and volume.

Changes in mechanisms proposed to mediate fat loss following an acute bout of high-intensity interval and endurance exercise.

The purpose of this study was to investigate the acute effects of endurance exercise (END; 65% V̇O2peak for 60 min) and high-intensity interval exercise (HIE; four 30 s Wingates separated by 4.5 min of active rest) on cardiorespiratory, hormonal, and subjective appetite measures that may account for the previously reported superior fat loss with low volume HIE compared with END. Recreationally active males (n = 18) completed END, HIE, and control (CON) protocols. On each test day, cardiorespiratory measures including oxygen uptake (V̇O2), respiratory exchange ratio (RER), and heart rate were recorded and blood samples were obtained at baseline (BSL), 60 min after exercise, and 180 min after exercise (equivalent times for CON). Subjective measures of appetite (hunger, fullness, nausea, and prospective consumption) were assessed using visual analogue scales, administered at BSL, 0, 60, 120, and 180 min after exercise. No significant differences in excess postexercise oxygen consumption (EPOC) were observed between conditions. RER was significantly (P < 0.05) depressed in HIE compared with CON at 60 min after exercise, yet estimates of total fat oxidation over CON were not different between HIE and END. No differences in plasma adiponectin concentrations between protocols or time points were present. Epinephrine and norepinephrine were significantly (P < 0.05) elevated immediately after exercise in HIE compared with CON. Several subjective measures of appetite were significantly (P < 0.05) depressed immediately following HIE. Our data indicate that increases in EPOC or fat oxidation following HIE appear unlikely to contribute to the reported superior fat loss compared with END.

Exercise persistence in the face of varying exercise challenges: A test of self-efficacy theory in working mothers

Self-regulatory efficacy (SRE) should influence persistence towards goals. Mothers attempting to exercise while managing work and young children (N = 49, Mage = 35.69, Mchildren = 1.88) were stratified into high or low concurrent SRE groups, then randomized to read a hypothetical scenario detailing numerous or minimal exercise barrier conditions. Consistent with self-efficacy theory, when exercise barriers were numerous, mothers with higher concurrent SRE demonstrated greater persistence towards exercise goals, and perceived concurrent management of exercise with their other valued goals as more positively challenging, than mothers with lower concurrent SRE.

Impact of High-Intensity Interval Duration on Perceived Exertion

PURPOSE RPE is increasingly being considered as a viable tool beyond its original use for monitoring in-task exercise intensity. Research indicates that anticipated, in-task, and postexercise RPE values are often notably different from one another. An important new consideration is how perceptions are impacted by high-intensity interval training (HIT). This study aims to compare RPE responses before, during, and after continuous and HIT exercise trials. METHODS Twenty (11 females and 9 males; mean ± SD age, 22 ± 4 yr) overweight (mean ± SD body mass index, 29 ± 3 kg·m(-2)) and unfit (mean ± SD V˙O2peak, 28 ± 5 mL·kg·min(-1)) participants completed a 20-min heavy continuous (HC) trial and three 24-min severe-intensity interval trials that utilized 1:1 work-to-recovery ratios: 30 s (Severe Interval-30), 60 s (Severe Interval-60), and 120 s (Severe Interval-120). Exertion was assessed using the Borg CR10 Scale. Data were analyzed using repeated-measures ANOVA and pairwise comparisons. RESULTS Anticipated exertion was highest in the Severe Interval-120 trial (5.8 ± 2.0; P < 0.05) compared with other trials. Exertion increased from beginning to end in all trials (P < 0.05), with the greatest increases observed within the HC trial. Session RPE for the Severe Interval-120 trial (6.4 ± 2.3) was higher than those for all other trials (P < 0.05), and session RPE for the Severe Interval-30 trial (3.7 ± 1.8) was lower than that for the HC trial (4.9 ± 1.6; P < 0.05). CONCLUSIONS These findings suggest that 30-s HIT protocols limit the perceptual drift that occurs during exercise, in comparison to HC exercise. Moreover, performing more intervals of shorter durations appears to produce lower postexercise RPE values than performing fewer intervals of longer duration and equal intensity. Because effort perception may influence behavior, these results could have implications for the prescription of interval training in overweight sedentary adults.

Commentary: Why sprint interval training is inappropriate for a largely sedentary population

Herein we present a commentary on Hardcastle et al. (2014) claim that interval training is “unlikely to be taken up by the majority of the sedentary population” (pg. 1).

Concurrent self-regulatory efficacy as a mediator of the goal: Exercise behaviour relationship

Examining exercise as a single goal-directed behaviour, without acknowledging the influence of other concurrent goals, may oversimplify the self-regulation needed in daily life. Concurrent self-regulatory efficacy, confidence in one’s ability to self-regulate the management of multiple goals, was explored as a potential mediator in the relationship between value of an exercise goal and future exercise behaviour. Undergraduate students were observed during a 4-week examination period where they faced greater than usual challenges to exercising regularly. Consistent with self-efficacy theory, concurrent self-regulatory efficacy was a significant partial mediator of the value of an exercise goal–exercise behaviour relationship.