Walter S. Hailes

Effects of post-exercise recovery in a cold environment on muscle glycogen, PGC-1α, and downstream transcription factors.

PURPOSE The purpose of this investigation was to determine the impact of post-exercise environmental cold exposure on muscle glycogen, PGC-1α, and downstream transcription factors. METHODS Eight males cycled for 1h and recovered in either 7 °C (cold) or 20 °C (room temp) environment for 4h. Muscle biopsies were obtained pre, post, and 4h post exercise for the analysis of muscle glycogen and mRNA. During recovery participants consumed 1.8 g kg⁻¹ of body weight of an oral dextrose solution immediately following the post biopsy and 2h into recovery. Blood samples were obtained post exercise and at 30, 60, 120, 150, 180, and 240 min post exercise for the analysis of serum glucose and insulin AUC. RESULTS Oxygen uptake was lower during room temp than during cold recovery (0.40 ± 0.05 L x min⁻¹ vs. 0.80 ± 0.12 L x min⁻¹; p<0.01). There was no effect of temperature on muscle glycogen recovery or glucose AUC. However, insulin AUC was greater during the room temp trial compared to the cold trial (5139 ± 1412 vs. 4318 ± 1272, respectively; p=0.025). PGC-1α gene expression was higher (p=0.029), but ERRα and NRF2 were lower (p=0.019 and p=0.046, respectively) after recovery in the cold. There were no differences in NRF1 (p=.173) or TFAM (p=0.694). CONCLUSIONS This investigation shows no effect of a cold recovery environment on glycogen re-synthesis but does demonstrate reduced ERRα and NRF2 mRNA despite elevations in PGC-1α mRNA when recovery post-exercise takes place in a cold environment.

Work Patterns Dictate Energy Demands and Thermal Strain During Wildland Firefighting

OBJECTIVE The purpose of this investigation was to characterize the effects of self-selected work activity on energy expenditure, water turnover, and thermal strain during wildland fire suppression. A secondary aim was to contrast current data with data collected 15 years ago using similar methods to determine whether job demands have changed. METHODS Participants (n=15, 26±3 years, 179±6 cm, 78.3±8.6 kg) were monitored for 3 days for total energy expenditure, water turnover, core and chest skin temperature, physical activity, and heart rate. Participants arrived to the mobile laboratory each morning, submitted a nude weight, ingested a temperature transmitter, provided a urine sample, and were equipped with a physiological and activity monitor. Participants completed live wildland fire suppression during their work shifts. RESULTS Mean core temperature was 37.6°±0.2°C, mean chest skin temperature was 34.1°±1.0°C, mean heart rate was 112±13 beats/min, and the mean physiological strain index score was 3.3±1.0. Wildland firefighters spent 49±8%, 39±6%, and 12±2% in the sedentary, light, and moderate-vigorous intensity categories, respectively. The mean total energy expenditure was 19.1±3.9 MJ/d, similar to 1997 (17.5±6.9 MJ/d). The mean water turnover in 2012 was 9.5±1.7 L/d, which was higher (P<.05) compared with 1997-98 (7.0±1.7 L/d). CONCLUSIONS Wildland firefighters do not induce consistently high cardiovascular and thermal strain while completing arduous work in a hot environment despite fairly high chest skin temperatures. The total energy expenditure in the current study suggests job demands are similar to those of 15 years ago, while the increased water turnover may reflect a change in drinking habits.

Local heat application enhances glycogenesis

The purpose of this study was to determine the impact of increased local muscle temperature independent of core temperature on glycogenesis during recovery from exercise when adequate carbohydrate provisions were supplied. Nine recreationally active males (age, 23 ± 4 years; height, 178 ± 6 cm; weight 79 ± 9 kg) cycled for 92 min and recovered for 4 h. During recovery the subjects legs were randomly assigned as the heated limb (heat pack application) and control limb (exposed to room air). Participants received 2 carbohydrate feedings (1.8 g·kg(-1) of body weight) at 0 and 2 h of recovery. Core temperature, intramuscular temperature, and leg circumference were monitored throughout recovery. Skeletal muscle biopsies samples of the vastus lateralis were obtained at the beginning and end of the 4-h recovery period on both legs and analyzed for glycogen and lactate. Core temperature did not change from throughout recovery. Muscle temperature in the heated limb was higher by 15 min and remained elevated throughout recovery compared with the control limb (p < 0.05). Leg circumference was not different between limbs. Lactate increased from postexercise to 4 h postexercise regardless of trial (p < 0.05). Muscle glycogen concentration increased with recovery and carbohydrate feeding in both limbs (p < 0.05) but was 22% higher in the heated limb compared with the control limb (p < 0.05). This study demonstrates increased glycogenesis when local muscle temperature is increased independent of core temperature.

Acute Hypoxia and Exercise-Induced Blood Oxidative Stress

Hypoxic exercise is characterized by workloads decrements. Because exercise and high altitude independently elicit redox perturbations, the study purpose was to examine hypoxic and normoxic steady-state exercise on blood oxidative stress. Active males (n = 11) completed graded cycle ergometry in normoxic (975 m) and hypoxic (3,000 m) simulated environments before programing subsequent matched intensity or workload steady-state trials. In a randomized counterbalanced crossover design, participants completed three 60-min exercise bouts to investigate the effects of hypoxia and exercise intensity on blood oxidative stress. Exercise conditions were paired as such; 60% normoxic VO(2)peak performed in a normoxic environment (normoxic intensity-normoxic environment, NI-NE), 60% hypoxic VO(2)peak performed in a normoxic environment (HI-NE), and 60% hypoxic VO(2)peak performed in a hypoxic environment (HI-HE). Blood plasma samples drawn pre (Pre), 0 (Post), 2 (2HR) and 4 (4HR) hr post exercise were analyzed for oxidative stress biomarkers including ferric reducing ability of plasma (FRAP), trolox equivalent antioxidant capacity (TEAC), lipid hydroperoxides (LOOH) and protein carbonyls (PCs). Repeated-measures ANOVA were performed, a priori significance of p ≤ .05. Oxygen saturation during the HI-HE trial was lower than NI-NE and HI-NE (p < .05). A Time × Trial interaction was present for LOOH (p = .013). In the HI-HE trial, LOOH were elevated for all time points post while PC (time; p = .001) decreased post exercise. As evidenced by the decrease in absolute workload during hypoxic VO(2)peak and LOOH increased during HI-HE versus normoxic exercise of equal absolute (HI-NE) and relative (NI-NE) intensities. Results suggest acute hypoxia elicits work decrements associated with post exercise oxidative stress.

The Effect of Environmental Temperature on Glucose and Insulin After an Oral Glucose Tolerance Test in Healthy Young Men

OBJECTIVE The purpose of this study was to compare glucose and insulin responses during an oral glucose tolerance test (OGTT) in cold (C), neutral (N), and hot (H) environments. METHODS Eleven males completed three 4-hour climate-controlled OGTT trials (C, 7.2°C; N, 22°C; and H, 43°C). Participants remained semireclined for 60 minutes before ingesting a 1.8 g/kg glucose beverage. Skin and rectal core temperatures were continuously monitored. Blood was collected just before glucose ingestion (time 0) and at 15, 30, 60, 90, 120, and 180 minutes, and analyzed for serum glucose, insulin, hematocrit, and hemoglobin. Expired gases were collected upon entering the chamber (-60 minutes), before glucose ingestion (0 minutes), and at 60, 120, and 180 minutes to determine V(O2) and respiratory exchange ratio. RESULTS Rectal core temperature was greater in the H condition compared with both C and N (P < .001). Rectal core temperature was not different between C and N, whereas skin temperature was different across all trials (H greater than N greater than C). The V(O2) was greater in C than in both H and N during all time points. Carbohydrate oxidation was greater in C compared with H and N (P < 0.001). Glucose was higher during H compared with C and N (P ≤ 0.002). Glucose was elevated in C compared with N. Insulin was higher in H compared with C (P = 0.009). Area under the curve for serum glucose was greater in H compared with C and N (P ≤ 0.001); however, there was no significant difference in area under the curve for insulin. CONCLUSIONS These data indicate that after an OGTT, glucose and insulin are elevated in a hot environment.

Human Skeletal Muscle mRNA Response to a Single Hypoxic Exercise Bout

BACKGROUND The ability to physically perform at high altitude may require unique strategies to acclimatize before exposure. The effect of acute hypoxic exposure on the metabolic response of the skeletal muscle may provide insight into the value of short-term preacclimatization strategies. OBJECTIVE To determine the human skeletal muscle response to a single acute bout of exercise in a hypoxic environment on metabolic gene expression. METHODS Eleven recreationally active male participants (24 ± 4 years, 173 ± 20 cm, 82 ± 12 kg, 15.2 ± 7.1% fat, 4.0 ± 0.6 L/min maximal oxygen consumption) completed two 1-hour cycling exercise trials at 60% of peak power followed by 4 hours of recovery in ambient environmental conditions (975 m) and at normobaric hypoxic conditions simulating 3000 m in a randomized counterbalanced order. Muscle biopsies were obtained from the vastus lateralis before exercise and 4 hours after exercise for real-time polymerase chain reaction analysis of select metabolic genes. RESULTS Gene expression of hypoxia-inducible factor 1 alpha, cytochrome c oxidase subunit 4, peroxisome proliferator-activated receptor gamma coactivator 1 alpha, hexokinase, phosphofructokinase, mitochondrial fission 1, and mitofusin-2 increased with exercise (P < .05) but did not differ with hypoxic exposure (P > .05). Optic atrophy 1 did not increase with exercise or differ between environmental conditions (P > .05). CONCLUSIONS The improvements in mitochondrial function reported with intermittent hypoxic training may not be explained by a single acute hypoxic exposure, and thus it appears that a longer period of preacclimatization than a single exposure may be required.

Seasonal heat acclimatization in wildland firefighters.

The purpose of this study was to determine changes in physiological markers of heat acclimatization across a 4-month wildland fire season. Wildland firefighters (WLFF) (n=12) and non-WLFF (n=14) were assessed pre- and post-season for body mass, percent body fat, and peak VO₂. Both groups completed a 60-min heat stress trial (walking at 50% of peak VO₂) in a climate controlled chamber (43.3 °C, 33% RH) pre and post-fire season (May through September). During the trials, core (Tc) and skin (Tsk) temperatures, heart rate (HR), physiological strain index (PSI), and rating of perceived exertion (RPE) were measured. There were no differences pre or post-season between the WLFF and non-WLFF groups in body mass, percent body fat, or peak V.O2. During the 73 days where the WLFF were involved in direct wildland fire suppression, daily high temperature for the WLFF was higher compared to the non-WLFF, 30.6 ± 5.4 °C and 26.9 ± 6.1 °C, respectively, p<0.05. Tc was lower at post-season compared to pre-season (p<0.05) for the WLFF at 30, 45, and 60 min (pre 30, 45, and 60: 37.9 ± 0.3, 38.3 ± 0.3 and 38.5 ± 0.3 °C, respectively; post 30, 45, and 60: 37.8 ± 0.3, 38.1 ± 0.3 and 38.2 ± 0.4 °C, respectively). For WLFF, PSI was lower (p<0.05) at 15, 30, 45, and 60 min at post-season compared to pre-season (4.2 ± 0.7, 5.6 ± 0.9, 6.5 ± 0.9, and 7.1 ± 1.1 for 15, 30, 45, and 60 min pre-season, respectively; 3.6 ± 0.8, 4.9 ± 1.0, 5.7 ± 1.2, 6.3 ± 1.3 for 15, 30, 45, and 60 min post-season, respectively). For WLFF, RPE was lower during the post-season trial at 30, 45, and 60 min (pre 30, 45, and 60: 11.7 ± 1.4, 12.3 ± 1.2, and 13.5 ± 1.4, respectively; post 30, 45, and 60: 10.7 ± 1.2, 11.3 ± 1.3, and 11.9 ± 1.5, respectively), p<0.05. There were no differences between pre and post-season for the non-WLFF for Tc and PSI, but RPE was lower at 15 min during the pre-season trial. WLFFs demonstrated significant decreases in Tc, PSI, and RPE during controlled heat stress after the season. Since an age and fitness-matched control group experienced no indication of heat acclimatization, it is suggested that the long-term occupational heat exposure accrued by the WLFFs was adequate to incur heat acclimatization.

Glycogen Levels in Wildland Firefighters During Wildfire Suppression

OBJECTIVE The purpose of this project was to determine the effects of wildfire suppression on muscle glycogen utilization in wildland firefighters (WLFFs). METHODS Wildland firefighters (n = 11) participated in the study. Muscle biopsies were obtained from the vastus lateralis pre- and post-work shift. Activity patterns were measured using an Actical activity monitor positioned on the chest. Food was consumed ad libitum and recorded using a food log and interview. Differences were analyzed using paired samples t-tests and relationships were assessed using Pearson r correlation coefficients. A significance level of p < .05 was set. RESULTS Body weight was similar pre- to post-work shift (85.9 ± 9.1 and 85.6 ± 8.8 kg, respectively). Muscle glycogen decreased from pre- to post-work shift, 101 ± 7 to 80 ± 5 mmol/kg wet wt, p < .05. Average activity counts were 175 ± 60 counts/min. Mean percent of time spent in each intensity category included: sedentary (74 ± 7%), light (21 ± 5%), and moderate/vigorous (5 ± 2%). There was a significant relationship between minutes completing vigorous activity and glycogen utilization (r = -.76, p < .05), and between minutes spent completing vigorous activity and pre-shift glycogen content (r = .79, p < .05). Kilocalorie intake during the work shift was 9.2 ± 2.9 MJ/d (2195 ± 699 kcal/d). CONCLUSIONS This study demonstrates the variety of self-selected nutritional and activity habits of WLFFs, and emphasizes the relationships between moderate/vigorous activity and muscle glycogen. The current data suggest that the food provided was adequate to maintain muscle glycogen levels pre- to post-work shift.

Factors of trainability and predictability associated with military physical fitness test success.

Cuddy, JS, Slivka, DR, Hailes, WS, and Ruby, BC. Factors of trainability and predictability associated with military physical fitness test success. J Strength Cond Res 25(12): 3486–3494, 2011—The purpose of this study was to determine the trainability of college-aged men using varied training programs and to assess factors associated with successfully passing a Special Operations Forces (SOF) physical fitness test (PFT). One hundred thirty-five male subjects were stratified into 3 training groups (run focused, calisthenic focused, or combined run and calisthenic) and were trained 3 times·per week for 12 weeks. Body composition and accelerometer activity patterns were measured pretraining and posttraining. The PFT performance (pull-ups, sit-ups, push-ups, and 1.5-mile run time) was measured weekly throughout the study period. The subjects exhibited reduced body fat (18.4 ± 7.7 to 16.9 ± 7.3), increased fat-free mass (66.1 ± 8.2 to 67.4 ± 7.9), reduced fat mass (15.8 ± 9.2 to 14.6 ± 8.9) from pretraining to posttraining, respectively (p < 0.05). All groups improved in each component of PFT performance with training (p < 0.05). There was a significant 20 ± 35% increase in 6-day average daily activity for the run-focused training group from pretraining and posttraining. The key indicators of a candidates potential to successfully reach SOF PFT standards (in 12 weeks) were determined to be as follows: enter the pipeline being able to run 2.4 km in ≤10:41 minutes, have a body fat percentage of ≤12.9%, and participate in a minimum of 30 min·d−1 of vigorous physical activity. Training an individuals relative run or calisthenic deficiency did not prove to be a better training approach compared with a program that emphasizes training both running and calisthenic activities.

Effects of Commercially Available Pneumatic Compression on Muscle Glycogen Recovery After Exercise

Abstract Keck, NA, Cuddy, JS, Hailes, WS, Dumke, CL, and Ruby, BC. Effects of commercially available pneumatic compression on muscle glycogen recovery after exercise. J Strength Cond Res 29(2): 379–385, 2015—The purpose of this study was to investigate the effects of pneumatic compression pants on postexercise glycogen resynthesis. Active male subjects (n = 10) completed 2 trials consisting of a 90-minute glycogen depleting ride, followed by 4 hours of recovery with either a pneumatic compression device (PCD) or passive recovery (PR) in a random counterbalanced order. A carbohydrate beverage (1.8 g·kg−1 bodyweight) was provided at 0 and 2 hours after exercise. Muscle biopsies (vastus lateralis) were obtained immediately and 4 hours after exercise for glycogen analyses. Blood samples were collected throughout recovery to measure glucose and insulin. Eight fingerstick blood samples for lactate were collected in the last 20 minutes of the exercise period and during the initial portion of the recovery period. Heart rate was monitored throughout the trial. During the PCD trial, subjects recovered using a commercially available recovery device (NormaTec PCD) operational at 0–60 and 120–180 minutes into recovery period. The same PCD was worn during the PR trial but was not turned on to create pulsatile pressures. There was no difference in muscle glycogen resynthesis during the recovery period (6.9 ± 0.8 and 6.9 ± 0.5 mmol·kg−1 wet wt·h−1 for the PR and PCD trials, respectively). Blood glucose, insulin, and lactate concentrations changed with respect to time but were not different between trials (p > 0.05). The use of PCD did not alter the rate of muscle glycogen resynthesis, blood lactate, or blood glucose and insulin concentrations associated with a postexercise oral glucose load.