John S. Cuddy

Human mRNA response to exercise and temperature.

The purpose of this research was to determine the mRNA response to exercise in different environmental temperatures. 9 recreationally active males (27±1 years, 77.4±2.7  kg, 13.5±1.5% fat, 4.49±0.15  L · min (-1) VO2 max) completed 3 trials consisting of 1 h cycling exercise at 60% Wmax followed by a 3 h recovery in the cold (7°C), room temperature (20°C), and hot (33°C) environments. Muscle biopsies were obtained pre, post, and 3 h post exercise for the analysis of glycogen and mRNA. Expired gases were collected to calculate substrate use. PGC-1α increased to a greater degree in the cold trial than in the room temperature trial (p=0.036) and the hot trial (p=0.006). PGC1-α mRNA was also higher after the room temperature trial than the hot trial (p=0.050). UCP3 and MFN2 mRNA increased with exercise (p<0.05), but were unaffected by temperature. COX was unaffected by exercise or temperature. Muscle glycogen decreased with exercise (p<0.05), but was no different among trials. Whole body VO2 was lower during exercise in the cold than exercise in the heat. However, VO2 was higher during recovery in the cold trial than in the room temperature and hot trials (p<0.05). This study presents evidence of PGC-1α temperature sensitivity in human skeletal muscle.

High work output combined with high ambient temperatures caused heat exhaustion in a wildland firefighter despite high fluid intake

The purpose of this case study is to examine the physiological/behavioral factors leading up to heat exhaustion in a male wildland firefighter during wildland fire suppression. The participant (24 years old, 173 cm, 70 kg, and 3 years firefighting experience) experienced heat exhaustion following 7 hours of high ambient temperatures and arduous work on the fire line during the month of August. At the time of the heat-related incident (HRI), core temperature was 40.1 °C (104.2 °F) and skin temperature was 34.4 °C (93.9 °F). His work output averaged 1067 counts·min(-1) (arbitrary units for measuring activity) for the 7 hours prior to the HRI, a very high rate of work over an extended time period during wildfire suppression. In the 2.5 hours leading up to the heat incident, he was exposed to a mean ambient temperature of 44.6 °C (112.3 °F), with a maximum temperature of 59.7 °C (139.5 °F). He consumed an average of 840 mL·h(-1) in the 7 hours leading up to the incident and took an average of 24 ± 11 drinks·h(-1) (total of 170 drinks). The combined effects of a high work rate and high ambient temperatures resulted in an elevated core temperature and a higher volume and frequency of drinking than typically seen in this population, ultimately ending in heat exhaustion and removal from the fire line. The data demonstrate that heat-related incidents can occur even with aggressive fluid intake during wildland fire suppression.

Efficacy of eat-on-move ration for sustaining physical activity, reaction time, and mood.

UNLABELLED Repeated carbohydrate feedings and caffeine have been shown to increase self-paced physical activity. Whether a field ration pack that promotes snacking of these items would enhance physical activity remains unclear. PURPOSE Evaluate the effectiveness of a ration pack consisting of eat-on-move items to promote snacking, as well as caffeine items, as a nutritional strategy to improve performance. METHODS Twenty-eight wildland firefighters consumed both an eat-on-move ration (first strike ration (FSR): 13.2 MJ, 420 g CHO, 665 mg caffeine daily) and entrée-based ration (meals, ready-to-eat (MRE): 11.9 MJ, 373 g CHO, 100 mg caffeine daily) for 2 d separated by 1 d. Diet order was counterbalanced. Outcome measurements included self-paced physical activity determined by actimetry, reaction time, number of eating occasions using dietary recall, and dietary intake from food wrapper collection. RESULTS Total eating episodes were higher with FSR compared with MRE (P = 0.013; mean +/- SD: 8.2 +/- 1.3 vs 7.6 +/- 1.1 episodes x 2 d(-1)), as were 2-d energy intake (22.0 +/- 2.4 vs 18.4 +/- 2.5 MJ; P < 0.01), carbohydrate intake (698 +/- 76 vs 546 +/- 82 mg; P < 0.01), self-reported caffeine intake (347 +/- 262 vs 55 +/- 65 mg; P < 0.01), and average end-shift salivary caffeine (1.6 +/- 1.9 vs 0.7 +/- 1.0 microg x mL(-1); P < 0.01). Total activity counts were higher (P = 0.046) when consuming FSR (507,833 +/- 129,130 counts per shift) compared with MRE (443,095 +/- 142,208 counts per shift). This was accomplished by spending a greater percentage of work shift with activity counts >1000 counts x min(-1) (21 +/- 8% vs 18 +/- 6%; P = 0.01) and less percent of work shift <50 counts x min(-1) (33 +/- 10% vs 38 +/- 10%; P = 0.01). CONCLUSIONS Delivery of energy and caffeine in a manner that promotes snacking behavior is advantageous for increasing self-selected physical activity during arduous labor.

Effects of 21 days of intensified training on markers of overtraining.

Slivka, DR, Hailes, WS, Cuddy, JS, and Ruby, BC. Effects of 21 days of intensified training on markers of overtraining. J Strength Cond Res 24(10): 2604-2612, 2010-The purpose of this study was to impose a period of quantifiable intensified training to determine if commonly used diagnostic markers of overtraining parallel changes in physical performance and thus overtraining status. Eight trained male cyclists (24 ± 1 years, 71 ± 3 kg, &OV0312;O2peak = 4.5 ± 0.1·L·min−1) performed 21 days (3,211 km) of intensified training in the field where volume and intensity were increased over normal training. Salivary IgA, testosterone, and cortisol, 1-hour time trial performance, heart rate response, and profile of mood states (POMS) were collected and analyzed throughout the 21-day training period. The POMS category vigor declined from day 1 to day 4 and remained lower throughout (p < 0.05). There were no other statistical changes in overtraining parameters. However, individuals who demonstrated 2 or more symptoms of overtraining at any point throughout the 21 days were considered symptomatic and had a lower (p < 0.05) &OV0312;O2peak (4.2 ± 0.1·vs. 4.7 ± 0.1 L·min−1) and lower (p < 0.05) average workload during the initial 1-hour time trial (253 ± 5 vs. 288 ± 14 W). Interestingly, the 1-hour time trial power in these individuals with symptoms of overtraining did not decline (p > 0.05). These data demonstrate that markers of overtraining do not parallel a decrease in performance and should be interpreted with caution.

Effects of an Electrolyte Additive on Hydration and Drinking Behavior During Wildfire Suppression

Abstract Objective.—The purpose of this study was to compare the effects of a water + electrolyte solution versus plain water on changes in drinking behaviors, hydration status, and body temperatures during wildfire suppression. Methods.—Eight participants consumed plain water, and eight participants consumed water plus an electrolyte additive during 15 hours of wildfire suppression. Participants wore a specially outfitted backpack hydration system equipped with a digital flow meter system affixed inline to measure drinking characteristics (drinking frequency and volume). Body weight and urine-specific gravity were collected pre- and postshift. Ambient, core, and skin temperatures were measured continuously using a wireless system. Work output was monitored using accelerometry. Results.—There were no differences between groups for body weight, drinking frequency, temperature data, activity, or urine-specific gravity (1.019 ± 0.007 to 1.023 ± 0.010 vs. 1.019 ± 0.005 to 1.024 ± 0.009 for water and water + electrolyte groups pre- and postshift, respectively; P < .05). There was a main effect for time for body weight, demonstrating an overall decrease (78.1 ± 13.3 and 77.3 ± 13.3 kg pre- and postshift, respectively; P < .05) across the work shift. The water group consumed more total fluid (main effect for treatment) than the water + electrolyte group (504 ± 472 vs. 285 ± 279 mL·h−1 for the water and water + electrolyte groups, respectively; P < .05). Conclusion.—The addition of an electrolyte mixture to plain water decreased the overall fluid consumption of the water + electrolyte group by 220 mL·h−1 (3.3 L·d−1). Supplementing water with electrolytes can reduce the amount of fluid necessary to consume and transport during extended activity. This can minimize carrying excessive weight, possibly reducing fatigue during extended exercise.

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.

Core-Temperature Sensor Ingestion Timing and Measurement Variability

CONTEXT Telemetric core-temperature monitoring is becoming more widely used as a noninvasive means of monitoring core temperature during athletic events. OBJECTIVE To determine the effects of sensor ingestion timing on serial measures of core temperature during continuous exercise. DESIGN Crossover study. SETTING Outdoor dirt track at an average ambient temperature of 4.4°C ± 4.1°C and relative humidity of 74.1% ± 11.0%. PATIENTS OR OTHER PARTICIPANTS Seven healthy, active participants (3 men, 4 women; age  =  27.0 ± 7.5 years, height  =  172.9 ± 6.8 cm, body mass  =  67.5 ± 6.1 kg, percentage body fat  =  12.7% ± 6.9%, peak oxygen uptake [Vo(2peak)]  =  54.4 ± 6.9 mL•kg⁻¹•min⁻¹) completed the study. INTERVENTION(S) Participants completed a 45-minute exercise trial at approximately 70% Vo(2peak). They consumed core-temperature sensors at 24 hours (P1) and 40 minutes (P2) before exercise. MAIN OUTCOME MEASURE(S) Core temperature was recorded continuously (1-minute intervals) using a wireless data logger worn by the participants. All data were analyzed using a 2-way repeated-measures analysis of variance (trial × time), Pearson product moment correlation, and Bland-Altman plot. RESULTS Fifteen comparisons were made between P1 and P2. The main effect of time indicated an increase in core temperature compared with the initial temperature. However, we did not find a main effect for trial or a trial × time interaction, indicating no differences in core temperature between the sensors (P1  =  38.3°C ± 0.2°C, P2  =  38.3°C ± 0.4°C). CONCLUSIONS We found no differences in the temperature recordings between the 2 sensors. These results suggest that assumed sensor location (upper or lower gastrointestinal tract) does not appreciably alter the transmission of reliable and repeatable measures of core temperature during continuous running in the cold.

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.