Effects of high-intensity intermittent exercise training on appetite regulation

Objective: An acute bout of high intensity intermittent exercise suppresses ad-libitum energy intake at the post-exercise meal. The present study examined the effects of 12 weeks of high intensity intermittent exercise training (HIIT) compared with moderate intensity continuous exercise training (MICT) on appetite regulation. Methods: Thirty overweight, inactive men (BMI: 27.2 +/- 1.3 kg/m2; V[spacing dot above]O2Peak: 35.3 +/- 5.3 mL.kg-1.min-1) were randomised to either HIIT or MICT (involving 12 weeks of training, 3 sessions per week) or a control group (CON) (n = 10 per group). Ad-libitum energy intake from a laboratory test meal was assessed following both a low-energy (LEP: 847 kJ) and a high-energy preload (HEP: 2438 kJ) pre and post-intervention. Perceived appetite and appetite-related blood variables were also measured. Results: There was no significant effect of the intervention period on energy intake at the test meal following the two different preloads (p >= 0.05). However, the 95% CI indicated a clinically meaningful decrease in energy intake after the HEP compared with LEP in response to HIIT (516 +/- 395 kJ decrease), but not for MICT or CON, suggesting improved appetite regulation. This was not associated with alterations in the perception of appetite or the circulating concentration of a number of appetite-related peptides or metabolites, although insulin sensitivity was enhanced with HIIT only (p = 0.003). Conclusion: HIIT appears to benefit appetite regulation in overweight men. The mechanisms for this remain to be elucidated

Response to ‘Post-exercise energy load and activities may affect subsequent ad libitum energy intake’

As pointed out by Thivel et al., the use of the fixed caloric load in the form of a liquid meal was to allow for a standardized comparison of the appetite-related blood variables. The authors suggest that the participants may have experienced different digestive acceptances and gastric emptying rates of the liquid meal, which may have affected energy intake in the subsequent ad libitum meal. While there is some evidence to suggest that gastric emptying may be affected by the intensity of exercise during exercise, there has been minimal research examining gastric emptying rates post exercise. The limited evidence available suggests that there are no differences in gastric emptying rates after either rest compared with low-intensity and high-intensity exercise. Regardless, any effect on gastric emptying rate does not change the conclusion that participants consumed less following high-intensity intermittent exercise—it simply offers an alternative explanation for the mechanism underlying this effect

Mild dehydration does not reduce postexercise appetite or energy intake

Purpose: It has now been established that exercise performed under various environmental conditions may affect acute energy intake and appetite-related hormones. The exact mechanism linking acute energy intake and exercise remains unknown, although indirect evidence suggests a possible role for hydration status. Therefore, the purpose of this study was to investigate the interaction of exercise and hydration status on subsequent energy intake and appetite-related hormones. Methods: In a randomized, counterbalanced design, 10 physically active males completed three experimental trials in a fasted state: exercise when hydrated (0%-1% of body mass), exercise when dehydrated (-1% to -2% of body mass), and a hydrated resting control. Exercise consisted of treadmill running for 45 min at 70% (V) over dotO(2peak). Participants were then given access to a buffet-style breakfast from which they could consume ad libitum. Blood was sampled regularly during trials for appetite-related hormones. Results: There were no significant differences in total energy intake between trials (P = 0.491); however, relative energy intake was significantly higher in the control (4839 +/- 415 kJ, P < 0.001) compared to hydrated (1749 +/- 403 kJ) and dehydrated exercise (1656 +/- 413 kJ) conditions. Exercise performed in a dehydrated state resulted in significantly lower concentrations of ghrelin compared with control (P = 0.045) and hydrated exercise conditions (P = 0.014). Conclusions: Exercise significantly decreased relative energy intake compared with resting control; however, energy intake (relative and total) was no different between the exercise conditions (dehydrated vs hydrated). Despite similar energy intake between trials, exercise in a dehydrated state resulted in a significantly lower concentration of ghrelin, a hormone responsible for stimulating appetite

High-intensity intermittent exercise attenuates ad-libitum energy intake

Objective: To examine the acute effects of high-intensity intermittent exercise (HIIE) on energy intake, perceptions of appetite and appetite-related hormones in sedentary, overweight men. Design: Seventeen overweight men (body mass index: 27.7±1.6 kg m−2; body mass: 89.8±10.1 kg; body fat: 30.0±4.3%; VO2peak: 39.2±4.8 ml kg−1 min−1) completed four 30-min experimental conditions using a randomised counterbalanced design. CON: resting control, MC: continuous moderate-intensity exercise (60% VO2peak), HI: high-intensity intermittent exercise (alternating 60 s at 100% VO2peak and 240 s at 50% VO2peak), VHI: very-high-intensity intermittent exercise (alternating 15 s at 170% VO2peak and 60 s at 32% VO2peak). Participants consumed a standard caloric meal following exercise/CON and an ad-libitum meal 70 min later. Capillary blood was sampled and perceived appetite assessed at regular time intervals throughout the session. Free-living energy intake and physical activity levels for the experimental day and the day after were also assessed. Results: Ad-libitum energy intake was lower after HI and VHI compared with CON (P=0.038 and P=0.004, respectively), and VHI was also lower than MC (P=0.028). Free-living energy intake in the subsequent 38 h remained less after VHI compared with CON and MC (P 0.050). These observations were associated with lower active ghrelin (P 0.050), higher blood lactate (P 0.014) and higher blood glucose (P 0.020) after VHI compared with all other trials. Despite higher heart rate and ratings of perceived exertion (RPE) during HI and VHI compared with MC (P 0.004), ratings of physical activity enjoyment were similar between all the exercise trials (P=0.593). No differences were found in perceived appetite between trials. Conclusions: High-intensity intermittent exercise suppresses subsequent ad-libitum energy intake in overweight inactive men. This format of exercise was found to be well tolerated in an overweight population

Energy intake and appetite-related hormones following acute aerobic and resistance exercise

Previous research has shown that resistance and aerobic exercise have differing effects on perceived hunger and circulating levels of appetite-related hormones. However, the effect of resistance and aerobic exercise on actual energy intake has never been compared. This study investigated the effect of an acute bout of resistance exercise, compared with aerobic exercise, on subsequent energy intake and appetite-regulating hormones. Ten active men completed 3 trials in a counterbalanced design: 45 min of resistance exercise (RES; free and machine weights), aerobic exercise (AER; running), or a resting control trial (CON). Following exercise or CON, participants had access to a buffet-style array of breakfast foods and drinks to consume ad libitum. Plasma concentrations of a range of appetite-regulating hormones were measured throughout each trial. Despite significantly higher energy expenditure with AER compared with RES (p < 0.05), there was no difference in total energy intake from the postexercise meal between trials (p = 0.779). Pancreatic polypeptide was significantly higher prior to the meal after both RES and AER compared with CON. In contrast, active ghrelin was lower following RES compared with both CON and AER (p ≤ 0.05), while insulin was higher following RES compared with CON (p = 0.013). In summary, the differential response of appetite-regulating hormones to AER and RES does not appear to influence energy intake in the postexercise meal. However, given the greater energy expenditure associated with AER compared with RES, AER modes of exercise may be preferable for achieving short-term negative energy balance

Heat added to Repeated-Sprint training in hypoxia does not affect cycling performance

Purpose: This study aimed to assess the influence of graded air temperatures during repeated-sprint training in hypoxia (RSH) on performance and physiological responses. Methods: Ten well-trained athletes completed one familiarization and 4 experimental sessions at a simulated altitude of 3000 m (0.144 FIO2) above sea level. Air temperatures utilized across the 4 experimental sessions were 20°C, 25°C, 30°C, and 35°C (all 50% relative humidity). The participants performed 3 sets of 5 × 10 seconds “all-out” cycle sprints, with 20 seconds of active recovery between sprints and 5 minutes of active recovery between sets (recovery intensity = 120 W). Core temperature, skin temperature, pulse oxygen saturation, heart rate, rating of perceived exertion, and thermal sensation were collected. Results: There were no differences between conditions for peak power, mean power, and total work in each set (P > .05). There were no condition × time interaction effects for any variables tested. The peak core temperature was highest at 30°C (38.06°C [0.31°C]). Overall, the pulse oxygen saturation was higher at 35°C than at 20°C (P < .001; d < 0.8), 25°C (P < .001; d = 1.12 ± 0.54, large), and 30°C (P < .001; d = 0.84 ± 0.53, large). Conclusion: Manipulating air temperature between 20°C and 35°C had no effect on performance or core temperature during a typical RSH session. However, the pulse oxygen saturation was preserved at 35°C, which may not be a desirable outcome for RSH interventions. The application of increased levels of ambient heat may require a different approach if augmenting the RSH stimulus is the desired outcome

Taking the plunge: When is best for hot water immersion to complement exercise in heat and hypoxia

This investigation assessed the psycho-physiological and performance effects of hot water immersion (HWI) implemented either before or after a repeated-sprint training in hypoxia (RSH) session conducted in the heat. Ten participants completed three RSH trials (3 × 10 × 5-s sprints), conducted at 40°C and simulated altitude of 3000 m. A 30-min monitoring period preceded and followed all exercise sessions. In PRE, the pre-exercise period was HWI, and the post-exercise period was seated rest in temperate conditions. This combination was reversed in POST. In CON, participants were seated in temperate conditions for both periods. Compared to CON, PRE elicited a reduction in power output during each repeated-sprint set (14.8–16.2%, all p < 0.001), and a significantly higher core temperature (Tc) during the pre-exercise period and throughout the exercise session (p < 0.001 and p = 0.025, respectively). In POST, power output and Tc until the end of exercise were similar to CON, with Tc higher at the conclusion of the post-exercise period (p < 0.001). Time across the entire protocol spent ≥38.5°C Tc was significantly longer in PRE (48.1 ± 22.5 min) than POST (31.0 ± 11.3 min, p = 0.05) and CON (15.8 ± 16.3 min, p < 0.001). Employing HWI following RSH conducted in the heat provides effective outcomes regarding physiological strain and cycling performance when compared to pre-exercise or no HWI

Repeated-sprint training in heat and hypoxia: Effect of exercise-to-rest ratio

The aim of this study was to investigate acute performance and physiological responses to the manipulation of exercise-to-rest ratio (E:R) during repeated-sprint hypoxic training (RSH) in hot conditions. Twelve male team-sport players completed two experimental sessions at a simulated altitude of ∼3000 m (FIO2 0.144), air temperature of 40°C and relative humidity of 50%. Exercise involved either 3×5×10-s (E:R1:2) or 3×10×5-s (E:R1:4) maximal cycling sprints interspersed with active recoveries at 120W (20-s between sprints, 2.5 and 5-min between sets for E:R1:2 and E:R1:4 respectively). Sessions were matched for overall sprint and total session duration (47.5-min). Peak and mean power output, and total work were greater in E:R1:4 than E:R1:2 (p  0.05).These results indicate E:R1:4 increased mechanical power output and core temperature compared to E:R1:2. Both protocols had different effects on measures of muscle oxygenation, with E:R1:2 generating greater muscle oxygen extraction and E:R1:4 producing more muscle oxygenation flux, which are both important signals for peripheral adaptation. We conclude that the E:R manipulation during RSH in the heat might be used to target different physiological and performance outcomes, with these findings forming a strong base for future mechanistic investigation

Increased air temperature during repeated-sprint training in hypoxia amplifies changes in muscle oxygenation without decreasing cycling performance

The present study aims to investigate the acute performance and physiological responses, with specific reference to muscle oxygenation, to ambient air temperature manipulation during repeated-sprint training in hypoxia (RSH). Thirteen male team-sport players completed one familiarisation and three experimental sessions at a simulated altitude of ∼3000 m (FIO2 0.144). Air temperatures utilised across the three experimental sessions were: 20°C, 35°C and 40°C (all 50% relative humidity). Participants performed 3 × 5 × 10-s maximal cycle sprints, with 20-s passive recovery between sprints, and 5 min active recovery between sets. There were no differences between conditions for cycling peak power, mean power, and total work (p>0.05). Peak core temperature (Tc) was not different between conditions (38.11 ± 0.36°C). Vastus lateralis muscle deoxygenation during exercise and reoxygenation during recovery was of greater magnitude in 35°C and 40°C than 20°C (p0.05). Exercise-induced increases in blood lactate concentration were higher in 35°C and 40°C than 20°C (p=0.010 and p=0.001, respectively). Integrating ambient temperatures up to 40°C into a typical RSH session had no detrimental effect on performance. Additionally, the augmented muscle oxygenation changes experienced during exercise and recovery in temperatures ≥35°C may indicate that the potency of RSH training is increased with additional heat. However, alterations to the training session may be required to generate a sufficient rise in Tc for heat training purposes

Temperature and hypoxia tolerance of selected fishes from a hyperthermal rockpool in the dry Tortugas, with notes on diversity and behavior

We documented the physical habitat characteristics and fish diversity of a hyperthermal rockpool on Loggerhead Key in the Dry Tortugas National Park during July 2000. Rockpool temperatures ranged from 30.5 °C to 35.8 °C and oxygen varied from 6.4 to 3.5 mg/L depending on depth and time of day. Seven fish species from five families inhabited the rockpool. Critical thermal maxima (CTMax) and critical oxygen minima (COM) were measured for three species. French grunt Haemulon flavolineatum was the most temperature tolerant fish (CTMax = 37.9 °C), followed by cocoa damselfish Pomacentrus variabilis (36.1 °C), and white mullet Mugil curema (35.0 °C), respectively. Cocoa damselfish were more tolerant of hypoxic conditions (COM = 0.8 mg/L) than either French grunt (1.2 mg/L) or white mullet (1.5 mg/L). French grunt and cocoa damselfish resorted to aquatic surface respiration at respective dissolved oxygen levels of 2.6 and 1.7 mg/L, whereas white mullet did not display this behavior at oxygen concentrations as low as 1.5 mg/L. High-temperature and low-oxygen responses of the three species were not exceptional, suggesting that behavior and not physiology is the major factor allowing Loggerhead Key fishes to exploit hyperthermal habitats