Twenty-Four Percent of Wildland Firefighters Reach Critical Levels of Serum Creatine Kinase During 80-Hour Critical Training.

INTRODUCTION: Wildland firefighters (WLFFs) must undergo a 2-wk critical training (CT) period prior to deployment to the field. This stress may result in clinical risks, including severe muscle damage and rhabdomyolysis. We aimed to document the effects of WLFFs' CT on physiologic markers of muscle damage and soreness. METHODS: Two interagency hotshot crews (n=25) were followed during spring 2022 for 80 h of training. Activity counts as well as records of upper-body (US) and lower-body (LS) muscle soreness were collected daily. Body weight (BW) and skinfold measurements were recorded on Day 1 (D1) and D11 to estimate body fat (BF) and lean body weight (LBW). Blood was collected on D1 and D11 to measure muscle and liver damage markers. RESULTS: Critical training resulted in significant elevations in creatine kinase (CK) (216.9±57.4 U/L vs 5166.4±1927.8 U/L, P=0.017) and lactate dehydrogenase (LDH) (175.5±4.0 IU/L vs 340.0±42.6 IU/L, P=0.001) despite no significant changes in BW, BF, LBW, cortisol, or testosterone. Main effects of time were seen in US and LS, peaking on D11 (US: 5.2±0.4 cm, P<0.001; LS: 5.5±0.4 cm, P<0.001). Those who spent the most minutes with activity counts of >1500 counts/min showed the greatest increase in CK and LDH. CONCLUSIONS: These data suggest that WLFFs undergo significant physiologic stressors, resulting in muscle soreness and damage during CT, with 6 of the 25 subjects reaching critical levels of serum CK. It appears that much of the muscle damage and soreness occurred because of unaccustomed WLFF job-specific tasks.

Wildland Firefighter Critical Training Elicits Positive Adaptations to Markers of Cardiovascular and Metabolic Health.

INTRODUCTION: The purpose of this study was to identify physiologic changes in body composition and resting metabolic markers of health across 2 wk of critical training (CT) in wildland firefighters (WLFFs). METHODS: Twenty-two male and 3 female participants were recruited from 2 hotshot crews across the western United States prior to the 2022 fire season and monitored over their 80-h CT. Body weight (BW) and skinfolds were recorded before and after CT to estimate body fat (BF) and lean body weight (LBW). Blood was analyzed for changes in hematocrit, hemoglobin, plasma volume, and resting values of a lipid and metabolic panel. RESULTS: The high physical demands of CT resulted in improvements in total cholesterol (-19.3 mg/dL, P<0.001), triglycerides (-34.4 mg/dL, P<0.001), low-density lipoprotein cholesterol (-18.1 mg/dL, P<0.001), very-low-density lipoprotein cholesterol (-5.2 mg/dL, P<0.001), high-density lipoprotein cholesterol (+4.0 mg/dL, P=0.002), non-high-density lipoprotein cholesterol (-19.3 mg/dL, P<0.001), and fasting glucose (-4.3 mg/dL, P=0.008) from before CT to after CT. Significant decreases in hemoglobin and hematocrit were also seen (P<0.001) with corresponding increases in estimated plasma volume (+6.1%, P<0.001). These alterations were seen despite maintenance of BW, LBW, and BF. Lower pretraining BF was associated with a greater magnitude of improvements in fasting glucose and cholesterol markers. CONCLUSIONS: The observed improvements in baseline metabolic and cardiovascular markers along with plasma volume expansion suggest a positive response to the physical stress of WLFF CT. It appears that higher preseason fitness was associated with greater adaptations to the CT stressor.

Cardiovascular and Blood Oxidative Stress Responses to Exercise and Acute Woodsmoke Exposure in Recreationally Active Individuals.

INTRODUCTION: Those who work and recreate outdoors experience woodsmoke exposure during fire season. Exercise during woodsmoke exposure harms the cardiovascular system, but the acute physiologic and biochemical responses are understudied. The purpose of this pilot laboratory-based study was to examine the effect of exercise during woodsmoke exposure on acute indicators of cardiovascular function, including heart rate variability (HRV), pulse wave velocity (PWV), blood pressure (BP), augmentation index (AIx), and blood oxidative stress. METHODS: Ten participants performed 2 moderate-intensity exercise (70% V˙O2 max) trials (clean air 0 µg·m-3, woodsmoke 250 µg·m-3) in a crossover design. HRV, PWV, BP, AIx, and blood oxidative stress were measured before, after, and 90 min after exercise for each trial. Blood oxidative stress was quantified through lipid damage (LOOH, 8-ISO), protein damage (3-NT, PC), and antioxidant capacity (TEAC). RESULTS: A 45-min woodsmoke exposure combined with moderate-intensity exercise did not result in a statistically significant difference in HRV, PWV, BP, AIx, or oxidative stress (P>0.05). CONCLUSIONS: Despite the known deleterious effects of smoke inhalation, moderate-intensity aerobic exercise while exposed to woodsmoke particulate matter (250 µg·m-3) did not result in a statistically significant difference in HRV, PWV, or blood oxidative stress in this methodologic context. Although findings do not negate the negative impact of woodsmoke inhalation, additional research approaches are needed to better understand the acute effects of smoke exposure on the cardiovascular system.

Alterations in Metabolic and Cardiovascular Risk Factors During Critical Training in Wildland Firefighters.

OBJECTIVE: To identify physiologic stressors related to cardiovascular disease via changes in metabolic, inflammatory, and oxidative stress biomarkers during 2 weeks of preseason training in wildland firefighters (WLFFs). METHODS: Participants were recruited from a local hotshot crew and monitored during preseason training. Fitness was assessed via the Bureau of Land Management fitness challenge. Venipuncture blood was collected on days 1, 4, 8, and 11 and analyzed for changes in a lipid and glucose panel, C-reactive protein, and oxidative stress markers 8-isoprostane (8ISO), 3-nitrotyrosine (3NT), lipid hydroperoxides (LOOH), and protein carbonyls. RESULTS: The high physical demands of training resulted in significant (P < 0.05) reductions in total cholesterol, glucose, and hemoglobin A1c. A main effect for time was observed in 8ISO, 3NT, and LOOH. CONCLUSIONS: Alterations in metabolic and oxidative stress markers suggest an acute, high-intensity physical stress during WLFF preseason training.

Muscle Damage and Overreaching During Wildland Firefighter Critical Training.

OBJECTIVE: To document the effects of wildland firefighter (WLFF) critical training (CT) on physiologic markers of muscle damage and acute overreaching. METHODS: Eighteen male and three female WLFFs were studied during an 11-day CT. Upper-body (US), lower-body (LS) muscle soreness and body weight (BW) were collected daily. Blood was collected on days 1, 4, 8, and 11 to measure creatine kinase (CK), lactate dehydrogenase (LDH), cortisol, and testosterone. Skinfolds were taken on days 1 and 11 to estimate body fat (BF) and lean body weight (LBW). RESULTS: CT resulted in a significant depression in BF and elevation in LBW, while main effects of time were seen in US, LS, CK, LDH, cortisol, and testosterone/cortisol ratio (P < 0.05). CONCLUSION: These data suggest WLFFs undergo significant physiological stressors resulting in muscle soreness, damage, and possible overreaching during CT.

Short term heat acclimation reduces heat stress, but is not augmented by dehydration.

Heat acclimation lowers physiological strain when exercising in the heat, and may be enhanced by promoting dehydration during acclimation. The purpose was to compare fluid intake during heat acclimation by promoting dehydration (DEH=0.5 mL kg-1 15 min-1, ~2.4% dehydration per acclimation session) compared to euhydration (EUH=2.0 mL kg-1 15 min-1, ~1.4% dehydration per acclimation session) following four heat acclimation bouts on thermal strain, and exercise performance. Thirteen males completed 90 min heat stress tests (HST) at 50% VO2max (40 °C, 30%RH) before and after three 90 min heat acclimation trials, involving consecutive bouts with 4-fold less fluid (DEH) or EUH. DEH and EUH trials were separated by 48 h and assigned in a random crossover design separated by a 5 week washout. Wildland firefighter (WLFF) Nomex: shirt, pants, and a cotton T-shirt baselayer were worn. Peak core temperature (Tc) from the HST significantly decreased following both DEH (39.5 ±â€¯0.1-39.0 ±â€¯0.1 °C: P < 0.001) and EUH acclimation (39.5 ±â€¯0.1-38.9 ±â€¯0.1 °C: P < 0.001). HR, RPE, physiological strain index (PSI), and total work (J) completed in a graded exercise test to exhaustion were improved (P < 0.001) in effect for acclimation, but not different when comparing DEH or EUH fluid delivery. SBF was unchanged (P = 0.313). Sweat rate increased greater following DEH (1.52 ±â€¯0.06-1.89 ±â€¯0.09 L h-1) compared to EUH acclimation (1.57 ±â€¯0.06-1.79 ±â€¯0.08 L h-1: P = 0.015). Resting plasma volume increased in effect for acclimation (P = 0.002). Aldosterone decreased in effect for acclimation (P < 0.001) at rest and following exercise, and total protein was unaffected (P = 0.83). In conclusion, short-term heat acclimation (~360 min) attenuates heat stress, and improves exercise capacity in the heat, and was not impaired nor improved by promoting DEH during acclimation.

Metabolic Demand of Hiking in Wildland Firefighting.

INTRODUCTION: The objective of this study was to document characteristics of hiking during wildland firefighter (WLFF) training and wildfire suppression. For the first time, the overall physical demands during wildland firefighting were evaluated in the field using global positioning systems coupled with wireless physiological monitoring and load carriage prediction models. METHODS: Male (n=116) and female (n=15) interagency hotshot crew and type II WLFFs on wildfires volunteered for this direct observation study. Participants' heart rate, internal temperature, speed, and elevation gain were monitored throughout training and during wildfire suppression. The Pandolf and Santee equations were used to predict metabolic rate to estimate oxygen consumption of uphill and downhill hiking. RESULTS: Equipment weight varied by crew type (type II: 24±9 kg and interagency hotshot crew: 28±6 kg; P<0.05). Grade of terrain was steepest during training hikes, and ingress hikes were statistically different from egress and training hikes (ingress: 4±9%, shift: 4±9%, egress: 1±8%, training hikes: 10±9%; P<0.01). Estimated oxygen consumption was highest during ingress hikes and was significantly different from all other hike types on fire assignments (ingress: 22±12, shift: 19±12, egress: 19±12 mL·kg-1·min-1; P=0.01). Oxygen consumption was higher during training hikes (34±14 mL·kg-1·min-1) than during job-related hikes (P<0.01). CONCLUSIONS: The greatest metabolic demand during wildfire assignments occurred during ingress hikes. On average, this was close to the estimated metabolic demand of the job qualification arduous pack test. However, greater metabolic demand occurred for periods during both shift (on the job) and training hikes. These data quantify the demands associated with actual wildland performance of WLFFs and can help define future work capacity testing and training procedures.

Comparison of Sports Drink Versus Oral Rehydration Solution During Exercise in the Heat.

INTRODUCTION: This study compared 2 commercially available beverages, an oral rehydration solution (ORS; 60.9 mM Na+; 3.4% carbohydrate) and a sports drink (SDS; 18.4 mM Na+; 5.9% carbohydrate), on hydration and metabolism during submaximal exercise in the heat. METHODS: Ten male subjects completed two 90-min exercise trials (39ºC, 30%) of walking at 50% VO2max followed by a 30-min rest period in the heat while wearing wildland firefighter personal protective clothing. After 45 min of exercise, fluid delivery by either ORS or SDS replaced 150% of sweat loss. Subjects continued the exercise for 45 additional minutes followed by a 30-min rest period. Blood samples were collected pre-exercise (0 min), post-exercise (90 min), and post-trial (120 min) to measure plasma volume (%) and blood glucose (mg·dL-1). Expired gases were collected twice for 3 min for substrate oxidation. RESULTS: The sweat rate and percent dehydration did not differ between the groups (P=0.86 and P=0.79, respectively). Changes in plasma volume did not differ (P=0.55). Hemoglobin levels significantly increased in both groups post-trial (P=0.009). Blood glucose was significantly greater post-trial in SDS versus ORS (116±19 vs 103±13 mg·dL-1, respectively; P=0.01). Fat oxidation was lower post-exercise in SDS vs ORS (0.38±0.1 vs 0.47±0.2 g·min-1, respectively; P=0.049). CONCLUSIONS: These data indicate no difference in fluid retention between ORS or SDS when supplemented during exercise in the heat. This implies that fluid volume, and not drink contents, may be more important when ingested during exercise in a hot environment.

Effect of Plyometrics on the Energy Cost of Running and MHC and Titin Isoforms.

UNLABELLED: Several training strategies such as plyometrics have been shown to improve running economy; however, its physiological basis remains elusive. PURPOSE: To examine the effect of plyometric training on the energy cost of running (ECR, J · kg(-1) · min(-1)), titin, and myosin heavy chain (MHC) isoforms. METHODS: Subjects were randomly assigned to a 6-wk plyometric treatment (P; n = 11) or control group (C; n = 11). Preintervention and postintervention outcomes included body composition, vertical jump, sit-and-reach, maximal oxygen consumption (VO2max), speed at onset of blood lactate, 3-km time trial performance, ECR, and a vastus lateralis muscle biopsy for protein analysis. RESULTS: Plyometric intervention resulted in improved time trial (P, 2.6% faster, P = 0.04; C, 1.6%, P = 0.17). VO2max improved in the P group (5.2%, P = 0.03), whereas the C group increased by 3.1% (P = 0.20). The ECR decreased in the P group as the result of 6 wk of plyometric training (P = 0.02 for stage 3), whereas it increased in the C group (P = 0.02 for stage 3). The ECR correlated strongly with performance at stages 2, 3, and 4 (r > 0.8, P < 0.001) independent of group. There was no significant main effect of group, time, or interaction on any of the protein isoforms analyzed. A negative correlation was found between the ECR at stage 7 and MHC IIa (r = -0.96, P < 0.001), and the ECR at stage 6 with titin isoform 1 (T1)/T2 ratio (r = -0.69, P = 0.007) independent of group. CONCLUSION: Six weeks of plyometric training improved running performance and the ECR despite no measurable changes in MHC and titin isoforms. However, higher MHC IIa and lower T1/T2 isoform ratios correlated to lower ECR.

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.

Postexercise Glycogen Recovery and Exercise Performance is Not Significantly Different Between Fast Food and Sport Supplements.

A variety of dietary choices are marketed to enhance glycogen recovery after physical activity. Past research informs recommendations regarding the timing, dose, and nutrient compositions to facilitate glycogen recovery. This study examined the effects of isoenergetic sport supplements (SS) vs. fast food (FF) on glycogen recovery and exercise performance. Eleven males completed two experimental trials in a randomized, counterbalanced order. Each trial included a 90-min glycogen depletion ride followed by a 4-hr recovery period. Absolute amounts of macronutrients (1.54 ± 0.27 g·kg-1 carbohydrate, 0.24 ± 0.04 g·kg fat-1, and 0.18 ±0.03g·kg protein-1) as either SS or FF were provided at 0 and 2 hr. Muscle biopsies were collected from the vastus lateralis at 0 and 4 hr post exercise. Blood samples were analyzed at 0, 30, 60, 120, 150, 180, and 240 min post exercise for insulin and glucose, with blood lipids analyzed at 0 and 240 min. A 20k time-trial (TT) was completed following the final muscle biopsy. There were no differences in the blood glucose and insulin responses. Similarly, rates of glycogen recovery were not different across the diets (6.9 ± 1.7 and 7.9 ± 2.4 mmol·kg wet weight- 1·hr-1 for SS and FF, respectively). There was also no difference across the diets for TT performance (34.1 ± 1.8 and 34.3 ± 1.7 min for SS and FF, respectively. These data indicate that short-term food options to initiate glycogen resynthesis can include dietary options not typically marketed as sports nutrition products such as fast food menu items.

Effects of commercially available pneumatic compression on muscle glycogen recovery after exercise.

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 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 wet wt·h 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.

Human skeletal muscle mRNAResponse 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.

Patients with type 1 diabetes oxidize fat at a greater rate than age- and sex-matched controls.

INTRODUCTION: Elevated patient blood glucose and exogenous insulin administration may affect substrate oxidation in patients with type 1 diabetes mellitus (T1DM); however, this has not been demonstrated with conviction. We examined substrate oxidation during incremental exercise in a group of subjects with T1DM and compared the results to those of an age- and sex-matched control group of subjects. METHODS: A group of subjects with T1DM (n = 29; 10 men, 19 women) was recruited for metabolic testing from a weeklong fitness camp. An age- and sex-matched control group of subjects (n = 29; 10 men, 19 women) was recruited from the local community. Subjects were required to avoid strenuous exercise for 48 hours and fast for 2 hours prior to metabolic testing. An incremental test to exhaustion on either a stationary cycle or treadmill was administered to all subjects. Maximum oxygen consumption of subjects was measured (T1DM subjects: 41.4 ± 1.9 mL/kg/min; control subjects: 48.4 ± 1.3 mL/kg/min). Blood glucose was recorded at 20 and 5 minutes before the exercise test, and at 5 and 20 minutes after the exercise test. RESULTS: The T1DM and control subjects were matched for age, height, weight, and body composition. Subject blood glucose levels were higher in the group of subjects with T1DM than the control group at all times measured (P < 0.001). At all relative intensities of exercise (50%-80% maximum oxygen consumption; P < 0.050), absolute fat oxidation was higher in the group of subjects with T1DM (P < 0.050) and absolute carbohydrate oxidation was higher in the control group. CONCLUSION: Our data indicate that subjects with T1DM oxidize fat at a higher rate and carbohydrates at a lower rate when compared with age- and sex-matched controls at the same relative intensity of exercise, despite the elevated pre-exercise blood glucose of subjects with T1DM.

Skeletal muscle metabolic gene response to carbohydrate feeding during exercise in the heat.

BACKGROUND: Heat stress down-regulates mitochondrial function, while carbohydrate supplementation attenuates the exercise induced stimulation of mitochondrial biogenesis in humans. The effects of exogenous carbohydrate during exercise in the heat on metabolic mRNA have not been investigated in humans. The purpose of this study was to determine the impact of exercise with and without carbohydrate supplementation on skeletal muscle metabolic response in the heat. METHODS: Eight recreationally active males (4.05 ± 0.2 L.min-1) completed 2 trials which included 1 hr of cycling at 70% workload max and 3 hr recovery in a hot environment. Both trials were conducted in a climate controlled environmental chamber (38°C and 40% RH). The trials differed by the consumption of either a 6% carbohydrate (CHO) containing beverage (8 ml.kg-1.hr-1) or placebo (P) during exercise in random order. Muscle biopsies were obtained from the vastus lateralis before exercise, immediately post-exercise and at the end of the 3 hr recovery period. Muscle was analyzed for muscle glycogen and mRNA related to metabolic and mitochondrial development (MFN2, PGC-1α, GLUT4, UCP3). Expired gases were measured to determine whole body substrate use during exercise. RESULTS: Carbohydrate oxidation and muscle glycogen utilization did not differ between trials, whereas fat oxidation was elevated during exercise in P. Exercise caused an increase in PGC-1α, and GLUT4 (P < 0.05) independent of exogenous carbohydrate provision. Carbohydrate consumption attenuated the mRNA response in UCP3 (P < 0.05). CONCLUSIONS: This study indicates that the provision of exogenous carbohydrate attenuates the stimulation of mRNA expression of UCP3 following exercise in the heat.

Substrate use and biochemical response to a 3,211-km bicycle tour in trained cyclists.

The purpose of this study was to assess the physiological adaptations in physically fit individuals to a period of intensified training. Ten trained males cycled outdoors ~170 km day(-1) on 19 out of 21 days. Expired gas was collected on days 1 and 21 during maximal graded exercise and used for the determination of gross efficiency and whole body substrate use. Muscle biopsies were obtained before and after exercise on days 2 and 22 for the determination of mtDNA/gDNA ratio, gene expression, metabolic enzyme activity and glycogen use. Muscle glycogen before and after exercise, fat oxidation, and gross efficiency increased, carbohydrate oxidation decreased (p < 0.05), and VO(2max) did not change over the 21 days of training. Citrate synthase (CS), ß-hydroxyacyl CoA dehydrogenase (ß-HAD) and cytochrome c oxidase (COX) enzyme activity did not change with training. CS and ß-HAD mRNA did not change with acute exercise or training. COX (subunit IV) mRNA increased with acute exercise (p < 0.05) but did not change over the 21 days. PGC-1α mRNA increased with acute exercise, but did not increase to the same degree on day 22 as it did on day 2 (p < 0.05). UCP3 mRNA decreased with training (p < 0.05). Acute exercise caused an increase in mitofusin2 (MFN2) mRNA (p < 0.05) and a trend for an increase in mtDNA/gDNA ratio (p = 0.057). However, training did not affect MFN2 mRNA or mtDNA/gDNA ratio. In response to 3,211 km of cycling, changes in substrate use and gross efficiency appear to be more profound than mitochondrial adaptations in trained individuals.

Effect of blueberry ingestion on natural killer cell counts, oxidative stress, and inflammation prior to and after 2.5 h of running.

Blueberries are rich in antioxidants known as anthocyanins, which may exhibit significant health benefits. Strenous exercise is known to acutely generate oxidative stress and an inflammatory state, and serves as an on-demand model to test antioxidant and anti-inflammatory compounds. The purpose of this study was to examine whether 250 g of blueberries per day for 6 weeks and 375 g given 1 h prior to 2.5 h of running at ∼72% maximal oxygen consumption counters oxidative stress, inflammation, and immune changes. Twenty-five well-trained subjects were recruited and randomized into blueberry (BB) (N = 13) or control (CON) (N = 12) groups. Blood, muscle, and urine samples were obtained pre-exercise and immediately postexercise, and blood and urine 1 h postexercise. Blood was examined for F2-isoprostanes for oxidative stress, cortisol, cytokines, homocysteine, leukocytes, T-cell function, natural killer (NK), and lymphocyte cell counts for inflammation and immune system activation, and ferric reducing ability of plasma for antioxidant capacity. Muscle biopsies were examined for glycogen and NFkB expression to evaluate stress and inflammation. Urine was tested for modification of DNA (8-OHDG) and RNA (5-OHMU) as markers of nucleic acid oxidation. A 2 (treatment) × 3 (time) repeated measures ANOVA was used for statistical analysis. Increases in F2-isoprostanes and 5-OHMU were significantly less in BB and plasma IL-10 and NK cell counts were significantly greater in BB vs. CON. Changes in all other markers did not differ. This study indicates that daily blueberry consumption for 6 weeks increases NK cell counts, and acute ingestion reduces oxidative stress and increases anti-inflammatory cytokines.

Relationship between muscle strength, power and stiffness and running economy in trained male runners.

PURPOSE: In this study, a comparison was made between muscle strength, power and muscle and tendon (km and kt respectively) stiffness of the triceps surae muscle group and running economy (RE) in trained male runners. METHODS: Twelve well-trained male runners (age = 21 +/- 2.7 y, height = 178.1 +/- 7.1 cm, body mass = 66.7 +/- 3.2 kg, VO2max = 68.3 +/- 4.3 mL x kg(-1) x min(-1), 5000-m time = 15:04 min:s) underwent passive stiffness testing using a free oscillation method. Muscle strength was determined via a maximal isometric squat test and power determined via a maximal countermovement jump (CMJ). On a separate day, subjects performed an incremental treadmill test and their RE, lactate threshold, and VO2max were determined. Fingertip blood lactate was determined at the end of each 3-min stage. Lactate threshold was defined as a nonlinear increase in lactate accumulation. RESULTS: A statistically significant correlation was found between km and VO2 at stage 6 (r = -0.69, P = .01). In addition, statistically significant correlations were observed between CMJ peak force production and VO2 at stage 2 (r = .66, P = .02), stage 3 (r = .70, P = .01), and stage 4 (r = .58, P = .04). No other statistically significant correlations were observed. CONCLUSION: These data suggest that greater muscle stiffness and less power are associated with greater RE. Future study in this area should focus on determining the mechanisms behind this relationship and how to best apply them to a running population through training techniques.