Greig Watson

Comparison of energy-restricted very low-carbohydrate and low-fat diets on weight loss and body composition in overweight men and women

ObjectiveTo compare the effects of isocaloric, energy-restricted very low-carbohydrate ketogenic (VLCK) and low-fat (LF) diets on weight loss, body composition, trunk fat mass, and resting energy expenditure (REE) in overweight/obese men and women.DesignRandomized, balanced, two diet period clinical intervention study. Subjects were prescribed two energy-restricted (-500 kcal/day) diets: a VLCK diet with a goal to decrease carbohydrate levels below 10% of energy and induce ketosis and a LF diet with a goal similar to national recommendations (%carbohydrate:fat:protein = ~60:25:15%).Subjects15 healthy, overweight/obese men (mean ± s.e.m.: age 33.2 ± 2.9 y, body mass 109.1 ± 4.6 kg, body mass index 34.1 ± 1.1 kg/m2) and 13 premenopausal women (age 34.0 ± 2.4 y, body mass 76.3 ± 3.6 kg, body mass index 29.6 ± 1.1 kg/m2).MeasurementsWeight loss, body composition, trunk fat (by dual-energy X-ray absorptiometry), and resting energy expenditure (REE) were determined at baseline and after each diet intervention. Data were analyzed for between group differences considering the first diet phase only and within group differences considering the response to both diets within each person.ResultsActual nutrient intakes from food records during the VLCK (%carbohydrate:fat:protein = ~9:63:28%) and the LF (~58:22:20%) were significantly different. Dietary energy was restricted, but was slightly higher during the VLCK (1855 kcal/day) compared to the LF (1562 kcal/day) diet for men. Both between and within group comparisons revealed a distinct advantage of a VLCK over a LF diet for weight loss, total fat loss, and trunk fat loss for men (despite significantly greater energy intake). The majority of women also responded more favorably to the VLCK diet, especially in terms of trunk fat loss. The greater reduction in trunk fat was not merely due to the greater total fat loss, because the ratio of trunk fat/total fat was also significantly reduced during the VLCK diet in men and women. Absolute REE (kcal/day) was decreased with both diets as expected, but REE expressed relative to body mass (kcal/kg), was better maintained on the VLCK diet for men only. Individual responses clearly show the majority of men and women experience greater weight and fat loss on a VLCK than a LF diet.ConclusionThis study shows a clear benefit of a VLCK over LF diet for short-term body weight and fat loss, especially in men. A preferential loss of fat in the trunk region with a VLCK diet is novel and potentially clinically significant but requires further validation. These data provide additional support for the concept of metabolic advantage with diets representing extremes in macronutrient distribution.

Ice Slurry Ingestion Increases Core Temperature Capacity and Running Time in the Heat

PURPOSE To investigate the effect of ice slurry ingestion on thermoregulatory responses and submaximal running time in the heat. METHODS On two separate occasions, in a counterbalanced order, 10 males ingested 7.5 g·kg(-1) of either ice slurry (-1°C) or cold water (4°C) before running to exhaustion at their first ventilatory threshold in a hot environment (34.0°C ± 0.2°C, 54.9% ± 5.9% relative humidity). Rectal and skin temperatures, HR, sweating rate, and ratings of thermal sensation and perceived exertion were measured. RESULTS Running time was longer (P = 0.001) after ice slurry (50.2 ± 8.5 min) versus cold water (40.7 ± 7.2 min) ingestion. Before running, rectal temperature dropped 0.66°C ± 0.14°C after ice slurry ingestion compared with 0.25°C ± 0.09°C (P = 0.001) with cold water and remained lower for the first 30 min of exercise. At exhaustion, however, rectal temperature was higher (P = 0.001) with ice slurry (39.36°C ± 0.41°C) versus cold water ingestion (39.05°C ± 0.37°C). During exercise, mean skin temperature was similar between conditions (P = 0.992), as was HR (P = 0.122) and sweat rate (P = 0.242). After ice slurry ingestion, subjects stored more heat during exercise (100.10 ± 25.00 vs 78.93 ± 20.52 W·m(-2), P = 0.005), and mean ratings of thermal sensation (P = 0.001) and perceived exertion (P = 0.022) were lower. CONCLUSIONS Compared with cold water, ice slurry ingestion lowered preexercise rectal temperature, increased submaximal endurance running time in the heat (+19% ± 6%), and allowed rectal temperature to become higher at exhaustion. As such, ice slurry ingestion may be an effective and practical precooling maneuver for athletes competing in hot environments.

Pre-cooling with ice slurry ingestion leads to similar run times to exhaustion in the heat as cold water immersion

Abstract The purpose of this study was to compare the effects of pre-exercise ice slurry ingestion and cold water immersion on submaximal running time in the heat. On three separate occasions, eight males ran to exhaustion at their first ventilatory threshold in the heat (34.0 ± 0.1°C, 52 ± 3% relative humidity) following one of three 30 min pre-exercise manoeuvres: (1) ice slurry ingestion; (2) cold water immersion; or (3) warm fluid ingestion (control). Running time was longer following cold water immersion (56.8 ± 5.6 min; P = 0.008) and ice slurry ingestion (52.7 ± 8.4 min; P = 0.005) compared with control (46.7 ± 7.2 min), but not significantly different between cold water immersion and ice slurry ingestion (P = 0.335). During exercise, rectal temperature was lower with cold water immersion from 15 and 20 min into exercise compared with control and ice slurry ingestion, respectively, and remained lower until 40 min (P = 0.001). At exhaustion rectal temperature was significantly higher following ice slurry ingestion (39.76 ± 0.36°C) compared with control (39.48 ± 0.36°C; P = 0.042) and tended to be higher than cold water immersion (39.48 ± 0.34°C; P = 0.065). As run times were similar between conditions, ice slurry ingestion may be a comparable form of pre-cooling to cold water immersion.

Effect of a 5-min cold-water immersion recovery on exercise performance in the heat

Background This study examined the effect of a 5-min cold-water immersion (14°C) recovery intervention on repeated cycling performance in the heat. Methods 10 male cyclists performed two bouts of a 25-min constant-paced (254 (22) W) cycling session followed by a 4-km time trial in hot conditions (35°C, 40% relative humidity). The two bouts were separated by either 15 min of seated recovery in the heat (control) or the same condition with 5-min cold-water immersion (5th—10th minute), using a counterbalanced cross-over design (CP1TT1 → CWI or CON → CP2TT2). Rectal temperature was measured immediately before and after both the constant-paced sessions and 4-km timed trials. Cycling economy and Vo2 were measured during the constant-paced sessions, and the average power output and completion times were recorded for each time trial. Results Compared with control, rectal temperature was significantly lower (0.5 (0.4)°C) in cold-water immersion before CP2 until the end of the second 4-km timed trial. However, the increase in rectal temperature (0.5 (0.2)°C) during CP2 was not significantly different between conditions. During the second 4-km timed trial, power output was significantly greater in cold-water immersion (327.9 (55.7) W) compared with control (288.0 (58.8) W), leading to a faster completion time in cold-water immersion (6.1 (0.3) min) compared with control (6.4 (0.5) min). Economy and Vo2 were not influenced by the cold-water immersion recovery intervention. Conclusion 5-min cold-water immersion recovery significantly lowered rectal temperature and maintained endurance performance during subsequent high-intensity exercise. These data indicate that repeated exercise performance in heat may be improved when a short period of cold-water immersion is applied during the recovery period.

Heat Acclimatization and Hydration Status of American Football Players During Initial Summer Workouts

This investigation evaluated the new National Collegiate Athletic Association model of heat acclimatization for football players using physiological, psychological, fluid balance, anthropometric, and nutritional variables. Eleven football players (20 ± 1 year, 1.88 ± 0.05 m, and 115.36 ± 18.85 kg) from a Division I football team were observed for the first 8 days of preseason practices. Measurements such as heart rate and gastrointestinal temperature (TGI) via telemetric sensor were taken before, 3 times during, and after practice daily. An average 1.39-kg (1.2%) decrease of body mass occurred from prepractice to postpractice (p ≤ 0.01). Consistent with mild body mass losses, urinary indices of hydration status (i.e., color, specific gravity, and osmolality) indicated mild fluid deficits. A significant increase (p ≤ 0.05) from pre-to postpractice was observed in urine color and urine specific gravity, but chronic hypohydration over the 8 days was not noted. The Environmental Symptoms Questionnaire (ESQ) postpractice score was significantly higher (p ≤ 0.05) than the prepractice score was, but averages did not differ across practice days. There was no difference in postpractice TGI measurements across days (p ≤ 0.05). Heart rate, TGI, and ESQ measurements indicated that football players experienced gradual heat acclimatization and enhanced heat tolerance, despite progressive increases of exercise variables, clothing, and environmental stressors.

Effect of cold-water immersion duration on body temperature and muscle function

Abstract This study compared the effect of 5, 10 and 20 min of cold-water (14°C) immersion on rectal and muscle temperature and neuromuscular function. Twelve cyclists performed four cycling time-to-exhaustion trials in hot conditions (40°C and 40%rh), followed 25 min later by cold-water immersion for 5, 10 or 20 min or 20 min in room temperature (24°C; control). Rectal temperature was measured continuously, and muscle temperature was measured before, immediately after and 45 min after the time-to-exhaustion-test, as well as before and after water immersion. Sixty-second maximal voluntary isometric torque and isokinetic torque of the knee extensors were measured before, immediately after and 55 min after time-to-exhaustion-test. A greater rate of decrease in rectal temperature was observed in all water immersion conditions 45–80 min after time-to-exhaustion-test compared with control. Compared with control, muscle temperature 45 min after time-to-exhaustion-test was lower for all water immersion conditions; however, muscle temperature was lower for the 10- and 20-min conditions compared with 5 min. Isometric torque measured 55 min after time-to-exhaustion-test was lower for all conditions. Isokinetic torque was lower for all conditions immediately and 55-min post-time-to-exhaustion-test. Of the durations measured, 5 min of cold-water immersion appeared as the most appropriate duration for reducing rectal temperature but limiting decreases in muscle temperature.

Current hydration guidelines are erroneous: dehydration does not impair exercise performance in the heat

Background Laboratory studies that support the hydration guidelines of leading governing bodies have shown that dehydration to only −2% of body mass can lead to increase in body temperature and heart rate during exercise, and decrease in performance. These studies, however, have been conducted in relatively windless environments (ie, wind speed <12.9 km/h), without participants being blinded to their hydration status. Aim To investigate the effect of blinded hydration status on cycling time-trial performance in the heat with ecologically valid facing wind speed conditions. Methods During three experimental trials, 10 cyclists were dehydrated to −3% body mass by performing 2 h of submaximal exercise (walking and cycling) in the heat, before being reinfused with saline to replace 100%, 33% or 0% of fluid losses, leaving them 0%, −2% or −3% hypohydrated, respectively. Participants then completed a 25 km time trial in the heat (33°C, 40% relative humidity; wind speed 32 km/h) during which their starting hydration status was maintained by infusing saline at a rate equal to their sweat rate. The treatment was participant-blinded and the order was randomised. Completion time, power output, heart rate, rectal temperature and perceptual variables were measured. Results While rectal temperature was higher beyond 17 km of the time trial in the −3% vs 0% conditions (38.9±0.3°C vs 38.6±0.3°C; p<0.05), no other differences between trials were shown. Conclusion When well-trained cyclists performed a 25 km cycling time trial under ecologically valid conditions and were blinded to their hydration status, performance, physiological and perceptual variables were not different between trials. These data do not support the residing basis behind many of the current hydration guidelines.

Effect of cold water immersion on repeated 1-km cycling performance in the heat

This study examined the effect of a short cold water immersion (CWI) intervention on rectal and muscle temperature, isokinetic strength and 1-km cycling time trial performance in the heat. Ten male cyclists performed a 1-km time trial at 35.0+/-0.3 degrees C and 40.0+/-3.0% relative humidity, followed by 20 min recovery sitting in either cold water (14 degrees C) for 5 min or in 35 degrees C air (control); a second 1-km time trial immediately followed. Peak and mean cycling power output were recorded for both time trials. Rectal and muscle temperature, and maximal isokinetic concentric torque of the knee extensors were measured before and immediately after the first and second time trials. Rectal temperature was not different between cold water immersion and control conditions at any time points. After the second time trial, however, muscle temperature was significantly lower (-1.3+/-0.7 degrees C) in cold water immersion compared with the control trial. While peak and mean power decreased from the first to second time trial in both conditions (-86+/-54 W and -24+/-16 W, respectively), maximal isokinetic concentric torque was similar between conditions at all time points. The 5 min cold water immersion intervention lowered muscle temperature but did not affect isokinetic strength or 1-km cycling performance.

Hormonal responses to a 160-km race across frozen Alaska

Background: Severe physical and environmental stress seems to have a suppressive effect on the hypothalamic–pituitary–gonadal (HPG) axis in men. Examining hormonal responses to an extreme 160-km competition across frozen Alaska provides a unique opportunity to study this intense stress. Objective: To examine hormonal responses to an ultra-endurance race. Methods: Blood samples were obtained from 16 men before and after racing and analyzed for testosterone, interleukin-6 (IL-6), growth hormone (GH) and cortisol. Six subjects (mean (SD) age 42 (7) years; body mass 78.9 (7.1) kg; height 1.78 (0.05) m raced by bicycle (cyclists) and 10 subjects (age 35 (9) years; body mass 77.9 (10.6) kg; height, 1.82 (0.05) m) raced by foot (runners). Mean (SD) finish times were 21.83 (6.27) and 33.98 (6.12) h, respectively. Results: In cyclists there were significant (p⩽0.05) mean (SD) pre-race to post-race increases in cortisol (254.83 (135.26) to 535.99 (232.22) nmol/l), GH (0.12 (0.23) to 3.21 (3.33) µg/ml) and IL-6 (2.36 (0.42) to 10.15 (3.28) pg/ml), and a significant decrease in testosterone (13.81 (3.19) to 5.59 (3.74) nmol/l). Similarly, in runners there were significant pre-race to post-race increases in cortisol (142.09 (50.74) to 452.21 (163.40) ng/ml), GH (0.12 (0.23) to 3.21 (3.33) µg/ml) and IL-6 (2.42 (0.68) to 12.25 (1.78) pg/ml), and a significant decrease in testosterone (12.32 (4.47) to 6.96 (3.19) nmol/l). There were no significant differences in the hormonal levels between cyclists and runners (p>0.05). Conclusions: These data suggest a suppression of the hypopituitary–gonadal axis potentially mediated by amplification of adrenal stress responses to such an ultra-endurance race in environmentally stressful conditions.

Postexercise muscle cooling enhances gene expression of PGC-1α

PURPOSE This study aimed to investigate the influence of localized muscle cooling on postexercise vascular, metabolic, and mitochondrial-related gene expression. METHODS Nine physically active males performed 30 min of continuous running at 70% of their maximal aerobic velocity, followed by intermittent running to exhaustion at 100% maximal aerobic velocity. After exercise, subjects immersed one leg in a cold water bath (10°C, COLD) to the level of their gluteal fold for 15 min. The contralateral leg remained outside the water bath and served as control (CON). Core body temperature was monitored throughout the experiment, whereas muscle biopsies and muscle temperature (Tm) measurements were obtained from the vastus lateralis before exercise (PRE), immediately postexercise (POST-EX, Tm only), immediately after cooling, and 3 h postexercise (POST-3H). RESULTS Exercise significantly increased core body temperature (PRE, 37.1°C ± 0.4°C vs POST-EX, 39.3°C ± 0.5°C, P < 0.001) and Tm in both CON (PRE, 33.9°C ± 0.7°C vs POST-EX, 39.1°C ± 0.5°C) and COLD legs (PRE, 34.2°C ± 0.9°C vs POST-EX, 39.4°C ± 0.3°C), respectively (P < 0.001). After cooling, Tm was significantly lower in COLD (28.9°C ± 2.3°C vs 37.0°C ± 0.8°C, P < 0.001) whereas PGC-1α messenger RNA expression was significantly higher in COLD at POST-3H (P = 0.014). Significant time effects were evident for changes in vascular endothelial growth factor (P = 0.038) and neuronal nitric oxide synthase (P = 0.019) expression. However, no significant condition effects between COLD and CON were evident for changes in both vascular endothelial growth factor and neuronal nitric oxide synthase expressions. CONCLUSIONS These data indicate that an acute postexercise cooling intervention enhances the gene expression of PGC-1α and may therefore provide a valuable strategy to enhance exercise-induced mitochondrial biogenesis.