Exercise adherence is affected by factors including perceptions of enjoyment, time availability, and intrinsic motivation. Approximately 50% of individuals withdraw from an exercise program within the first 6 mo of initiation, citing lack of time as a main influence. Time efficient exercise such as high intensity interval training (HIIT) may provide an alternative to moderate intensity continuous exercise (MICT) to elicit substantial health benefits. This study examined differences in enjoyment, affect, and perceived exertion between MICT and HIIT. Twelve recreationally active men and women (age = 29.5 ± 10.7 yr, VO₂max = 41.4 ± 4.1 mL/kg/min, BMI = 23.1 ± 2.1 kg/m²) initially performed a VO₂max test on a cycle ergometer to determine appropriate workloads for subsequent exercise bouts. Each subject returned for two additional exercise trials, performing either HIIT (eight 1 min bouts of cycling at 85% maximal workload (Wmax) with 1 min of active recovery between bouts) or MICT (20 min of cycling at 45% Wmax) in randomized order. During exercise, rating of perceived exertion (RPE), affect, and blood lactate concentration (BLa) were measured. Additionally, the Physical Activity Enjoyment Scale (PACES) was completed after exercise. Results showed higher enjoyment (p = 0.013) in response to HIIT (103.8 ± 9.4) versus MICT (84.2 ± 19.1). Eleven of 12 participants (92%) preferred HIIT to MICT. However, affect was lower (p<0.05) and HR, RPE, and BLa were higher (p<0.05) in HIIT versus MICT. Although HIIT is more physically demanding than MICT, individuals report greater enjoyment due to its time efficiency and constantly changing stimulus. Trial Registration: NCT:02981667.

Caffeine is the most widely used drug in the world, commonly ingested in coffee, tea, soda, and energy drinks. Its ability to enhance muscular work has been apparent since the early 1900s. Caffeine typically increases endurance performance; however, efficacy of caffeine ingestion for short-term high-intensity exercise is equivocal, which may be explained by discrepancies in exercise protocols, dosing, and subjects' training status and habitual caffeine intake found across studies. The primary aim of this review is to critically examine studies that have tested caffeine's ability to augment performance during exercise dependent on nonoxidative metabolism such as sprinting, team sports, and resistance training. A review of the literature revealed 29 studies that measured alterations in short-term performance after caffeine ingestion. Each study was critically analyzed using the Physiotherapy Evidence Database (PEDro) scale. The mean PEDro score was 7.76 +/- 0.87. Eleven of 17 studies revealed significant improvements in team sports exercise and power-based sports with caffeine ingestion, yet these effects were more common in elite athletes who do not regularly ingest caffeine. Six of 11 studies revealed significant benefits of caffeine for resistance training. Some studies show decreased performance with caffeine ingestion when repeated bouts are completed. The exact mechanism explaining the ergogenic effect of caffeine for short-term exercise is unknown.

(HIIT) on cardiovascular function, cardiorespiratory fitness, and muscular force. Active, young (age and body fat = 25.3 ± 4.5 years and 14.3 ± 6.4%) men and women (N = 20) of a similar age, physical activity, and maximal oxygen uptake (V̇o2max) completed 6 sessions of HIIT consisting of repeated Wingate tests over a 2- to 3-week period. Subjects completed 4 Wingate tests on days 1 and 2, 5 on days 3 and 4, and 6 on days 5 and 6. A control group of 9 men and women (age and body fat = 22.8 ± 2.8 years and 15.2 ± 6.9%) completed all testing but did not perform HIIT. Changes in resting blood pressure (BP) and heart rate (HR), V̇o2max, body composition, oxygen (O2) pulse, peak, mean, and minimum power output, fatigue index, and voluntary force production of the knee flexors and extensors were examined pretraining and posttraining. Results showed significant (p < 0.05) improvements in V̇o2max, O2 pulse, and Wingate-derived power output with HIIT. The magnitude of improvement in V̇o2max was related to baseline V̇o2max (r = −0.44, p = 0.05) and fatigue index (r = 0.50, p < 0.05). No change (p > 0.05) in resting BP, HR, or force production was revealed. Data show that HIIT significantly enhanced V̇o2max and O2 pulse and power output in active men and women....

Olney, N, Wertz, T, LaPorta, Z, Mora, A, Serbas, J, and Astorino, TA. Comparison of acute physiological and psychological responses between moderate-intensity continuous exercise and three regimes of high intensity interval training. J Strength Cond Res 32(8): 2130–2138, 2018—High-intensity interval training (HIIT) elicits similar physiological adaptations as moderate-intensity continuous training (MICT) despite less time commitment. However, there is debate whether HIIT is more aversive than MICT. This study compared physiological and perceptual responses between MICT and 3 regimes of HIIT. Nineteen active adults (age = 24.0 ± 3.3 years) unfamiliar with HIIT initially performed ramp exercise to exhaustion to measure maximal oxygen uptake (V̇o ₂max) and determine workload for subsequent sessions, whose order was randomized. Sprint interval training (SIT) consisted of six 20-second bouts of “all-out” cycling at 140% of maximum watts (Wmax). Low-volume HIIT (HIIT_LV) and high-volume HIIT (HIIT_HV) consisted of eight 60-second bouts at 85% Wmax and six 2-minute bouts at 70% Wmax, respectively. Moderate-intensity continuous training consisted of 25 minutes at 40% Wmax. Across regimes, work was not matched. Heart rate (HR), V̇o ₂, blood lactate concentration (BLa), affect, and rating of perceived exertion (RPE) were assessed during exercise. Ten minutes postexercise, Physical Activity Enjoyment (PACES) was measured via a survey. Results revealed significantly higher (p ≤ 0.05) V̇o ₂, HR, BLa, and RPE in SIT, HIIT_LV, and HIIT_HV vs. MICT. Despite a decline in affect during exercise (p < 0.01) and significantly lower affect (p ≤ 0.05) during all HIIT regimes vs. MICT at 50, 75, and 100% of session duration, PACES was similar across regimes (p = 0.65), although it was higher in women (p = 0.03). Findings from healthy adults unaccustomed to interval training demonstrate that HIIT and SIT are perceived as enjoyable as MICT despite being more aversive.