Beyond change scores: Employing an improved statistical approach to analyze the impact of entry fitness on physical performance during British Army basic training in men and women.

The aim was to use a robust statistical approach to examine whether physical fitness at entry influences performance changes between men and women undertaking British Army basic training (BT). Performance of 2 km run, seated medicine ball throw (MBT) and isometric mid-thigh pull (MTP) were assessed at entry and completion of Standard Entry (SE), Junior Entry-Short (JE-Short), and Junior Entry-Long (JE-Long) training for 2350 (272 women) recruits. Performance change was analyzed with entry performance as a covariate (ANCOVA), with an additional interaction term allowing different slopes for courses and genders (p < 0.05). Overall, BT courses saw average improvements in 2 km run performance (SE: -6.8% [-0.62 min], JE-Short: -4.6% [-0.43 min], JE-Long: -7.7% [-0.70 min]; all p < 0.001) and MBT (1.0-8.8% [0.04-0.34 m]; all p < 0.05) and MTP (4.5-26.9% [6.5-28.8 kg]; all p < 0.001). Regression models indicate an expected form of "regression to the mean" whereby test performance change was negatively associated with entry fitness in each course (those with low baseline fitness exhibit larger training improvements; all interaction effects: p < 0.001, η p 2 $$ {\eta}_{\mathrm{p}}^2 $$ > 0.006), particularly for women. However, when matched for entry fitness, men displayed considerable improvements in all tests, relative to women. Training courses were effective in developing recruit physical fitness, whereby the level of improvement is, in large part, dependent on entry fitness. Factors including age, physical maturity, course length, and physical training, could also contribute to the variability in training response between genders and should be considered when analyzing and/or developing physical fitness in these cohorts for future success of military job-task performance.

Cognitive, Psychophysiological, and Perceptual Responses to a Repeated Military-Specific Load Carriage Treadmill Simulation.

BACKGROUND: Dismounted military operations require soldiers to complete cognitive tasks whilst undertaking demanding and repeated physical taskings. OBJECTIVE: To assess the effects of repeated fast load carriage bouts on cognitive performance, perceptual responses, and psychophysiological markers. METHODS: Twelve civilian males (age, 28 ± 8 y; stature, 186 ± 6 cm; body mass 84.3 ± 11.1 kg; V̇O2max, 51.5 ± 6.4 mL·kg-1·min-1) completed three ∼65-min bouts of a Fast Load Carriage Protocol (FLCP), each interspersed with a 65-min recovery period, carrying a representative combat load of 25 kg. During each FLCP, cognitive function was assessed using a Shoot/Don't-Shoot Task (SDST) and a Military-Specific Auditory N-Back Task (MSANT), along with subjective ratings. Additional psychophysiological markers (heart rate variability, salivary cortisol, and dehydroepiandrosterone-sulfate concentrations) were also measured. RESULTS: A main effect of bout on MSANT combined score metric (p < .001, Kendall's W = 69.084) and for time on the accuracy-speed trade-off parameter of the SDST (p = .025, Ñ 2 = .024) was evident. These likely changes in cognitive performance were coupled with subjective data indicating that participants perceived that they increased their mental effort to maintain cognitive performance (bout: p < .001, Ñ 2 = .045; time: p < .001, Ñ 2 = .232). Changes in HRV and salivary markers were also evident, likely tracking increased stress. CONCLUSION: Despite the increase in physiological and psychological stress, cognitive performance was largely maintained; purportedly a result of increased mental effort. APPLICATION: Given the likely increase in dual-task interference in the field environment compared with the laboratory, military commanders should seek approaches to manage cognitive load where possible, to maintain soldier performance.

Association between external training loads and injury incidence during 44 weeks of military training.

Military training is physically arduous and associated with high injury incidence. Unlike in high-performance sport, the interaction between training load and injury has not been extensively researched in military personnel. Sixty-three (43 men, 20 women; age 24 ± 2 years; stature 1.76 ± 0.09 m; body mass 79.1 ± 10.8 kg) British Army Officer Cadets undergoing 44 weeks of training at the Royal Military Academy Sandhurst volunteered to participate. Weekly training load (cumulative 7-day moderate-vigorous physical activity [MVPA], vigorous PA [VPA], and the ratio between MVPA and sedentary-light PA [SLPA; MVPA:SLPA]) was monitored using a wrist-worn accelerometer (GENEActiv, UK). Self-report injury data were collected and combined with musculoskeletal injuries recorded at the Academy medical center. Training loads were divided into quartiles with the lowest load group used as the reference to enable comparisons using odds ratios (OR) and 95% confidence intervals (95% CI). Overall injury incidence was 60% with the most common injury sites being the ankle (22%) and knee (18%). High (load; OR; 95% CI [>2327 mins; 3.44; 1.80-6.56]) weekly cumulative MVPA exposure significantly increased odds of injury. Similarly, likelihood of injury significantly increased when exposed to low-moderate (0.42-0.47; 2.45 [1.19-5.04]), high-moderate (0.48-0.51; 2.48 [1.21-5.10]), and high MVPA:SLPA loads (>0.51; 3.60 [1.80-7.21]). High MVPA and high-moderate MVPA:SLPA increased odds of injury by ~2.0 to 3.5 fold, suggesting that the ratio of workload to recovery is important for mitigating injury occurrence.

The effect of sex, menstrual cycle phase and oral contraceptive use on intestinal permeability and ex-vivo monocyte TNFα release following treatment with lipopolysaccharide and hyperthermia.

PURPOSE: Investigate the impact of sex, menstrual cycle phase and oral contraceptive use on intestinal permeability and ex-vivo tumour necrosis factor alpha (TNFα) release following treatment with lipopolysaccharide (LPS) and hyperthermia. METHODS: Twenty-seven participants (9 men, 9 eumenorrheic women (MC) and 9 women taking an oral contraceptive pill (OC)) completed three trials. Men were tested on 3 occasions over 6 weeks; MC during early-follicular, ovulation, and mid-luteal phases; OC during the pill and pill-free phase. Intestinal permeability was assessed following a 4-hour dual sugar absorption test (lactulose: rhamnose). Venous blood was collected each trial and stimulated with 100 µg·mL-1 LPS before incubation at 37 °C and 40 °C and analysed for TNFα via ELISA. RESULTS: L:R ratio was higher in OC than MC (+0.003, p = 0.061) and men (+0.005, p = 0.007). Men had higher TNFα responses than both MC (+53 %, p = 0.004) and OC (+61 %, p = 0.003). TNFα release was greater at 40 °C than 37 °C (+23 %, p < 0.001). CONCLUSIONS: Men present with lower resting intestinal barrier permeability relative to women regardless of OC use and displayed greater monocyte TNFα release following whole blood treatment with LPS and hyperthermia. Oral contraceptive users had highest intestinal permeability however, neither permeability or TNFα release were impacted by the pill cycle. Although no statistical effect was seen in the menstrual cycle, intestinal permeability and TNFα release were more variable across the phases.

Nutrition and Physical Activity During British Army Officer Cadet Training: Part 1-Energy Balance and Energy Availability.

Military training is characterized by high daily energy expenditures which are difficult to match with energy intake, potentially resulting in negative energy balance (EB) and low energy availability (EA). The aim of this study was to quantify EB and EA during British Army Officer Cadet training. Thirteen (seven women) Officer Cadets (mean ± SD: age 24 ± 3 years) volunteered to participate. EB and EA were estimated from energy intake (weighing of food and food diaries) and energy expenditure (doubly labeled water) measured in three periods of training: 9 days on-camp (CAMP), a 5-day field exercise (FEX), and a 9-day mixture of both CAMP and field-based training (MIX). Variables were compared by condition and gender with a repeated-measures analysis of variance. Negative EB was greatest during FEX (-2,197 ± 455 kcal/day) compared with CAMP (-692 ± 506 kcal/day; p < .001) and MIX (-1,280 ± 309 kcal/day; p < .001). EA was greatest in CAMP (23 ± 10 kcal·kg free-fat mass [FFM]-1·day-1) compared with FEX (1 ± 16 kcal·kg FFM-1·day-1; p = .002) and MIX (10 ± 7 kcal·kg FFM-1·day-1; p = .003), with no apparent difference between FEX and MIX (p = .071). Irrespective of condition, there were no apparent differences between gender in EB (p = .375) or EA (p = .385). These data can be used to inform evidenced-based strategies to manage EA and EB during military training, and enhance the health and performance of military personnel.

Nutrition and Physical Activity in British Army Officer Cadet Training Part 2-Daily Distribution of Energy and Macronutrient Intake.

Dietary intake and physical activity impact performance and adaptation during training. The aims of this study were to compare energy and macronutrient intake during British Army Officer Cadet training with dietary guidelines and describe daily distribution of energy and macronutrient intake and estimated energy expenditure. Thirteen participants (seven women) were monitored during three discrete periods of military training for 9 days on-camp, 5 days of field exercise, and 9 days of a mixture of the two. Dietary intake was measured using researcher-led food weighing and food diaries, and energy expenditure was estimated from wrist-worn accelerometers. Energy intake was below guidelines for men (4,600 kcal/day) and women (3,500 kcal/day) during on-camp training (men = -16% and women = -9%), field exercise (men = -33% and women = -42%), and combined camp and field training (men and women both -34%). Carbohydrate intake of men and women were below guidelines (6 g·kg-1·day-1) during field exercise (men = -18% and women = -37%) and combined camp and field training (men = -33% and women = -39%), respectively. Protein intake was above guidelines (1.2 kcal·kg-1·day-1) for men and women during on-camp training (men = 48% and women = 39%) and was below guidelines during field exercise for women only (-27%). Energy and macronutrient intake during on-camp training centered around mealtimes with a discernible sleep/wake cycle for energy expenditure. During field exercise, energy and macronutrient intake were individually variable, and energy expenditure was high throughout the day and night. These findings could be used to inform evidenced-based interventions to change the amount and timing of energy and macronutrient intake around physical activity to optimize performance and adaptations during military training.

Accuracy of Metabolic Cost Predictive Equations During Military Load Carriage.

ABSTRACT: Vine, CA, Coakley, SL, Blacker, SD, Doherty, J, Hale, B, Walker, EF, Rue, CA, Lee, BJ, Flood, TR, Knapik, JJ, Jackson, S, Greeves, JP, and Myers, SD. Accuracy of metabolic cost predictive equations during military load carriage. J Strength Cond Res 36(5): 1297-1303, 2022-To quantify the accuracy of 5 equations to predict the metabolic cost of load carriage under ecologically valid military speed and load combinations. Thirty-nine male serving infantry soldiers completed thirteen 20-minute bouts of overground load carriage comprising 2 speeds (2.5 and 4.8 km·h-1) and 6 carried equipment load combinations (25, 30, 40, 50, 60, and 70 kg), with 22 also completing a bout at 5.5 km·h-1 carrying 40 kg. For each speed-load combination, the metabolic cost was measured using the Douglas bag technique and compared with the metabolic cost predicted from 5 equations; Givoni and Goldman, 1971 (GG), Pandolf et al. 1997 (PAN), Santee et al. 2001 (SAN), American College of Sports Medicine 2013 (ACSM), and the Minimum-Mechanics Model (MMM) by Ludlow and Weyand, 2017. Comparisons between measured and predicted metabolic cost were made using repeated-measures analysis of variance and limits of agreement. All predictive equations, except for PAN, underpredicted the metabolic cost for all speed-load combinations (p < 0.001). The PAN equation accurately predicted metabolic cost for 40 and 50 kg at 4.8 km·h-1 (p > 0.05), underpredicted metabolic cost for all 2.5 km·h-1 speed-load combinations as well as 25 and 30 kg at 4.8 km·h-1, and overpredicted metabolic cost for 60 and 70 kg at 4.8 km·h-1 (p < 0.001). Most equations (GG, SAN, ACSM, and MMM) underpredicted metabolic cost while one (PAN) accurately predicted at moderate loads and speeds, but overpredicted or underpredicted at other speed-load combinations. Our findings indicate that caution should be applied when using these predictive equations to model military load carriage tasks.

Plasma uptake of selected phenolic acids following New Zealand blackcurrant extract supplementation in humans.

New Zealand blackcurrant (NZBC) extract is a rich source of anthocyanins and in order to exert physiological effects, the anthocyanin-derived metabolites need to be bioavailable in vivo. We examined the plasma uptake of selected phenolic acids following NZBC extract supplementation alongside maintaining a habitual diet (i.e. not restricting habitual polyphenol intake). Twenty healthy volunteers (nine females, age: 28 ± 7 years, height 1.73 ± 0.09 m, body mass 73 ± 11 kg) consumed a 300 mg NZBC extract capsule (CurraNZ®; anthocyanin content 105 mg) following an overnight fast. Venous blood samples were taken pre and 1, 1.5, 2, 3, 4, 5, and 6 h post-ingestion of the capsule. Reversed-phase high-performance liquid chromatography (HPLC) was used for analysis of two dihydroxybenzoic acids [i.e. vanillic acid (VA) and protocatechuic acid (PCA)] and one trihydroxybenzoic acid [i.e. gallic acid (GA)] in plasma following NZBC extract supplementation. Habitual anthocyanin intake was 168 (95%CI:68-404) mg⋅day-1 and no associations were observed between this and VA, PCA, and GA plasma uptake by the NZBC extract intake. Plasma time-concentration curves revealed that GA, and PCA were most abundant at 4, and 1.5 h post-ingestion, representing a 261% and 320% increase above baseline, respectively, with VA remaining unchanged. This is the first study to demonstrate that an NZBC extract supplement increases the plasma uptake of phenolic acids GA, and PCA even when a habitual diet is followed in the days preceding the experimental trial, although inter-individual variability is apparent.

Field validation of The Heat Strain Decision Aid during military load carriage.

OBJECTIVES: We aimed to determine the agreement between actual and predicted core body temperature, using the Heat Strain Decision Aid (HSDA), in non-Ground Close Combat (GCC) personnel wearing multi terrain pattern clothing during two stages of load carriage in temperate conditions. DESIGN: Cross-sectional. METHODS: Sixty participants (men = 49, women = 11, age 31 ± 8 years; height 171.1 ± 9.0 cm; body mass 78.1 ± 11.5 kg) completed two stages of load carriage, of increasing metabolic rate, as part of the development of new British Army physical employment standards (PES). An ingestible gastrointestinal sensor was used to measure core temperature. Testing was completed in wet bulb globe temperature conditions; 1.2-12.6 °C. Predictive accuracy and precision were analysed using individual and group mean inputs. Assessments were evaluated by bias, limits of agreement (LoA), mean absolute error (MAE), and root mean square error (RMSE). Accuracy was evaluated using a prediction bias of ±0.27 °C and by comparing predictions to the standard deviation of the actual core temperature. RESULTS: Modelling individual predictions provided an acceptable level of accuracy based on bias criterion; where the total of all trials bias ± LoA was 0.08 ± 0.82 °C. Predicted values were in close agreement with the actual data: MAE 0.37 °C and RMSE 0.46 °C for the collective data. Modelling using group mean inputs were less accurate than using individual inputs, but within the mean observed. CONCLUSION: The HSDA acceptably predicts core temperature during load carriage to the new British Army non-GCC PES, in temperate conditions.

Effect of losartan on performance and physiological responses to exercise at high altitude (5035 m).

OBJECTIVE: Altitude-related and exercise-related elevations in blood pressure (BP) increase the likelihood of developing pulmonary hypertension and high-altitude illness during high-altitude sojourn. This study examined the antihypertensive effect and potential exercise benefit of the angiotensin II receptor antagonist losartan when taken at altitude. METHODS: Twenty participants, paired for age and ACE genotype status, completed a double-blinded, randomised study, where participants took either losartan (100 mg/day) or placebo for 21 days prior to arrival at 5035 m (Whymper Hut, Mt Chimborazo, Ecuador). Participants completed a maximal exercise test on a supine cycle ergometer at sea level (4 weeks prior) and within 48 hours of arrival to 5035 m (10-day ascent). Power output, beat-to-beat BP, oxygen saturation (SpO2) and heart rate (HR) were recorded during exercise, with resting BP collected from daily medicals during ascent. Before and immediately following exercise at 5035 m, extravascular lung water prevalence was assessed with ultrasound (quantified via B-line count). RESULTS: At altitude, peak power was reduced relative to sea level (p<0.01) in both groups (losartan vs placebo: down 100±29 vs 91±28 W, p=0.55), while SpO2 (70±6 vs 70±5%, p=0.96) and HR (146±21 vs 149±24 bpm, p=0.78) were similar between groups at peak power, as was the increase in systolic BP from rest to peak power (up 80±37 vs 69±33 mm Hg, p=0.56). Exercise increased B-line count (p<0.05), but not differently between groups (up 5±5 vs 8±10, p=0.44). CONCLUSION: Losartan had no observable effect on resting or exercising BP, exercise-induced symptomology of pulmonary hypertension or performance at 5035 m.

No Effect of New Zealand Blackcurrant Extract on Recovery of Muscle Damage Following Running a Half-Marathon.

New Zealand blackcurrant (NZBC) contains anthocyanins, known to moderate blood flow and display anti-inflammatory properties that may improve recovery from exercise-induced muscle damage. The authors examined whether NZBC extract supplementation enhances recovery from exercise-induced muscle damage after a half-marathon race. Following a randomized, double-blind, independent groups design, 20 (eight women) recreational runners (age 30 ± 6 years, height 1.73 ± 0.74 m, body mass 68.5 ± 7.8 kg, half-marathon finishing time 1:56:33 ± 0:18:08 hr:min:s) ingested either two 300-mg/day capsules of NZBC extract (CurraNZ™) or a visually matched placebo, for 7 days prior to and 2 days following a half-marathon. Countermovement jump performance variables, urine interleukin-6, and perceived muscle soreness and fatigue were measured pre, post, and at 24 and 48 hr after the half-marathon and analyzed using a mixed linear model with statistical significance set a priori at p < .05. The countermovement jump performance variables were reduced immediately post-half-marathon (p < .05), with all returning to pre-half-marathon levels by 48 hr, except the concentric and eccentric peak force and eccentric duration, with no difference in response between groups (p > .05). Urine interleukin-6 increased 48-hr post-half-marathon in the NZBC group only (p < .01) and remained unchanged compared with pre-half-marathon levels in the placebo group (p > .05). Perceived muscle soreness and fatigue increased immediately post-half-marathon (p < .01) and returned to pre-half-marathon levels by 48 hr, with no difference between groups (p > .05). Supplementation with NZBC extract had no effect on the recovery of countermovement jump variables and perceptions of muscle soreness or fatigue following a half-marathon in recreational runners.

A job task analysis to describe the physical demands of specialist paramedic roles in the National Ambulance Resilience Unit (NARU).

BACKGROUND: The National Ambulance Resilience Unit (NARU) works on behalf of each National Health Service (NHS) Ambulance Trust in England to strengthen national resilience and improve patient outcome in challenging pre-hospital scenarios. OBJECTIVE: To conduct a Job Task Analysis and describe the physical demands of NARU roles. METHODS: A focus group was conducted to describe the physically demanding tasks performed by NARU personnel. Subsequently, the physical demands of the identified tasks were measured in 34 NARU personnel (29 male and 5 female). RESULTS: Eleven criterion tasks were identified; Swift Water Rescue (SWR), Re-board Inflatable Boat (RBIB), Set up Decontamination Tent (SDT), Clinical Decontamination (CD), Movement in Gas Tight Suits (MGTS), Marauding Terrorist Fire Arms (MTFA), Over Ground Rescue (OGR), Unload Incidence Response Unit Vehicle (UIRUV), Above Ground Rescue (AGR), Over Rubble Rescue (ORR) and Subterranean Rescue (SR). The greatest cardiovascular strain was measured during SWR, MGTS, and MTFA. The most thermally challenging tasks were the MTFA, CD, SR and OGR. The greatest muscular strength requirements were during MTFA and OGR. CONCLUSIONS: All five components of fitness (aerobic endurance, anaerobic endurance, muscular strength, muscular endurance and mobility) were required for successful completion of the physically demanding tasks performed by NARU personnel.

Acetazolamide reduces exercise capacity following a 5-day ascent to 4559 m in a randomised study.

OBJECTIVE: To assess whether acetazolamide (Az), used prophylactically for acute mountain sickness (AMS), alters exercise capacity at high altitude. METHODS: Az (500 mg daily) or placebo was administered to 20 healthy adults (aged 36±20 years, range 21-77), who were paired for age, sex, AMS susceptibility and weight, in a double-blind, randomised manner. Participants ascended over 5 days to 4559 m, then exercised to exhaustion on a bicycle ergometer, while recording breath-by-breath gas measurements. Comparisons between groups and matched pairs were done via Mann-Whitney U and Pearson's χ2 tests, respectively. RESULTS: Comparing paired individuals at altitude, those on Az had greater reductions in maximum power output (Pmax) as a percentage of sea-level values (65±14.1 vs 76.6±7.4 (placebo); P=0.007), lower VO2max (20.7±5.2 vs 24.6±5.1 mL/kg/min; P<0.01), smaller changes from rest to Pmax for VO2 (9.8±6.2 vs 13.8±4.9 mL/kg/min; P=0.04) and lower heart rate at Pmax (154±25 vs 167±16, P<0.01) compared with their placebo-treated partners. Correlational analysis (Pearson's) indicated that with increasing age Pmax (r=-0.83: P<0.005) and heart rate at Pmax (r=-0.71, P=0.01) reduced more in those taking Az. CONCLUSION: Maximum exercise performance at altitude was reduced more in subjects taking Az compared with placebo, particularly in older individuals. The age-related effect may reflect higher tissue concentrations of Az due to reduced renal excretion. Future studies should explore the effectiveness of smaller Az doses (eg, 250 mg daily or less) in older individuals to optimise the altitude-Az-exercise relationships.

Cardiorespiratory and metabolic responses after exercise-induced muscle damage: the influence of lowered glycogen.

BACKGROUND: We examined the effect of early-onset of muscle damage and low muscle glycogen on cardiorespiratory and metabolic responses to low-intensity exercise. METHODS: Twelve men cycled for 10 min at 50% maximal oxygen uptake before, and 12 h after a morning downhill run (five, 8 min bouts at -12% gradient, with 2 min rests) under normal (NORM) and lowered glycogen (LOW) conditions, following a cross-over design with conditions separated by six weeks. Cardiorespiratory responses were recorded, with oxidation measures derived from stoichiometry equations. RESULTS: Muscle damage symptoms post-downhill (0 h) were similar between conditions. Carbon dioxide ventilatory equivalent increased 12 h post-downhill for LOW (P<0.05), but not NORM (P=0.7). A trend towards decreased respiratory exchange ratio (RER) was shown 12 h post-downhill for LOW (1.00±0.07 to 0.89±0.12, P=0.06), but not NORM (0.94±0.11 to 0.94±0.08; P=0.6). Twelve hours after LOW downhill running fat oxidation increased (0.21±0.18 g·min-1 to 0.36±0.27 g·min-1; P<0.05) and carbohydrate oxidation decreased (2.68±0.52 g·min-1 to 1.98±0.75 g·min-1; P<0.05); NORM oxidation rates were unchanged (fat: 0.26±0.18 g·min-1 to 0.33±0.18 g·min-1; P=0.5; carbohydrate: 2.51±0.49 g·min-1 to 2.29±0.47 g·min-1; P=0.3). CONCLUSIONS: Cycling at low-intensity 12 h post-downhill running with lowered muscle glycogen increased fat oxidation, decreased carbohydrate oxidation and elevated carbon dioxide ventilation. Damaging exercise with reduced glycogen availability increases fat utilization during subsequent low-intensity exercise as little as 12 h later.

Hypoxia Impairs Muscle Function and Reduces Myotube Size in Tissue Engineered Skeletal Muscle.

Contemporary tissue engineered skeletal muscle models display a high degree of physiological accuracy compared with native tissue, and therefore may be excellent platforms to understand how various pathologies affect skeletal muscle. Chronic obstructive pulmonary disease (COPD) is a lung disease which causes tissue hypoxia and is characterized by muscle fiber atrophy and impaired muscle function. In the present study we exposed engineered skeletal muscle to varying levels of oxygen (O2 ; 21-1%) for 24 h in order to see if a COPD like muscle phenotype could be recreated in vitro, and if so, at what degree of hypoxia this occurred. Maximal contractile force was attenuated in hypoxia compared to 21% O2 ; with culture at 5% and 1% O2 causing the most pronounced effects with 62% and 56% decrements in force, respectively. Furthermore at these levels of O2 , myotubes within the engineered muscles displayed significant atrophy which was not seen at higher O2 levels. At the molecular level we observed increases in mRNA expression of MuRF-1 only at 1% O2 whereas MAFbx expression was elevated at 10%, 5%, and 1% O2 . In addition, p70S6 kinase phosphorylation (a downstream effector of mTORC1) was reduced when engineered muscle was cultured at 1% O2 , with no significant changes seen above this O2 level. Overall, these data suggest that engineered muscle exposed to O2 levels of ≤5% adapts in a manner similar to that seen in COPD patients, and thus may provide a novel model for further understanding muscle wasting associated with tissue hypoxia. J. Cell. Biochem. 118: 2599-2605, 2017. © 2017 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Effect of eccentric exercise with reduced muscle glycogen on plasma interleukin-6 and neuromuscular responses of musculus quadriceps femoris.

Eccentric exercise can result in muscle damage and interleukin-6 (IL-6) secretion. Glycogen availability is a potent stimulator of IL-6 secretion. We examined effects of eccentric exercise in a low-glycogen state on neuromuscular function and plasma IL-6 secretion. Twelve active men (23 ± 4 yr, 179 ± 5 cm, 77 ± 10 kg, means ± SD) completed two downhill treadmill runs (gradient, -12%, 5 × 8 min; speed, 12.1 ± 1.1 km/h) with normal (NG) and reduced muscle glycogen (RG) in randomized order and at least 6 wk apart. Muscle glycogen was reduced using an established cycling protocol until exhaustion and dietary manipulation the evening before the morning run. Physiological responses were measured up to 48 h after the downhill runs. During recovery, force deficits of musculus quadriceps femoris by maximal isometric contractions were similar. Changes in low-frequency fatigue were larger with RG. Voluntary activation and plasma IL-6 levels were similar in recovery between conditions. It is concluded that unaccustomed, damaging eccentric exercise with low muscle glycogen of the m. quadriceps femoris 1) exacerbated low-frequency fatigue but 2) had no additional effect on IL-6 secretion. Neuromuscular impairment after eccentric exercise with low muscle glycogen appears to have a greater peripheral component in early recovery.

The application of maximal heart rate predictive equations in hypoxic conditions.

PURPOSE: Peak heart rate (HRpeak) is a common tool used in exercise prescription for groups in which maximal exercise intensity is contraindicated; however, the application of this method in normobaric hypoxia is unknown. Therefore, this study investigated the response of HRpeak and the application of predictive HRpeak equations to prescribe exercise intensity in acute normobaric hypoxia. Results were used to examine whether age-derived HRpeak predictive equations are valid in hypoxic conditions. METHODS: Fifteen untrained (eight men) volunteers (age 22 ± 2 years; peak rate of oxygen consumption 46.3 ± 7.0 ml kg(-1) min(-1)) completed incremental cycle ergometer tests (randomised order) to measure HRpeak at sea-level (SL (ambient inspiratory oxygen fraction (FIO2) 0.209)) and four normobaric hypoxic conditions FIO2: 0.185, 0.165, 0.142, 0.125 (≈1,000-4,000 m). RESULTS: HRpeak was similar across all conditions (SL, 182 ± 13; 0.185, 178 ± 11; 0.165, 177 ± 9; 0.142, 178 ± 9; 0.125, 175 ± 10 b min(-1)) despite a reduction in oxygen saturation with increasing hypoxia (SL, 95 ± 5; 0.185, 95 ± 2; 0.165, 92 ± 2; 0.142, 88 ± 3; 0.125, 82 ± 4 %; P ≤ 0.05). The HRpeak was overestimated by all equations compared to the measured value (P < 0.05). Four equations overestimated HRpeak in all conditions (P < 0.01); two in four conditions (0.185, 0.165, 0.142, 0.125; P < 0.01); and two in three conditions (0.165, 0.142, 0.125; P < 0.01). CONCLUSION: The overestimation of HRpeak by commonly used age-derived predictive equations in normobaric hypoxic conditions suggests that despite possible contraindications researchers should directly measure HRpeak whenever possible if it is to be used to prescribe exercise intensities.

Neuromuscular responses to mild-muscle damaging eccentric exercise in a low glycogen state.

The aim of this study was to examine the effect of low muscle glycogen on the neuromuscular responses to maximal eccentric contractions. Fourteen healthy men (22 ± 3 years) performed single-leg cycling (20 min at ~75% maximal oxygen uptake (V̇O2 max); eight 90 s sprints at a 1:1 work-to-rest ratio (5% decrements from 90% to 55% V̇O2 max until exhaustion) the evening before 100 eccentric (1.57 rads(-1)) with reduced (RED) and normal glycogen (NORM). Neuromuscular responses were measured during and up to 48 h after with maximal voluntary and involuntary (twitch, 20 Hz and 50 Hz) isometric contractions. During eccentric contractions, peak torque decreased (RED: -16.1 ± 2.5%; NORM: -6.2 ± 5.1%) and EMG frequency increased according to muscle length. EMG activity decreased for RED only. After eccentric contractions, maximal isometric force was reduced up to 24h for NORM (-13.5 ± 5.8%) and 48 h for RED (-7.4 ± 10.9%). Twelve hours after eccentric contractions, twitch force and the 20:50 Hz ratio were decreased for RED but not for NORM. Immediate involuntary with prolonged voluntary force loss suggests that reduced glycogen is associated with increased susceptibility to mild muscle-damaging eccentric exercise with contributions of peripheral and central mechanisms to be different during recovery.

Force and acceleration characteristics of military foot drill: implications for injury risk in recruits.

BACKGROUND: Foot drill involving marching and drill manoeuvres is conducted regularly during basic military recruit training. Characterising the biomechanical loading of foot drill will improve our understanding of the contributory factors to lower limb overuse injuries in recruits. AIM: Quantify and compare forces, loading rates and accelerations of British Army foot drill, within and between trained and untrained personnel. METHODS: 24 trained soldiers (12 men and 12 women; TRAINED) and 12 civilian men (UNTRAINED) performed marching and five drill manoeuvres on force platforms; motion capture recorded tibial position. Peak vertical impact force (PF), peak vertical loading rate (PLR), expressed as multiples of body weight (BW) and peak tibial impact acceleration (PTA) were recorded. RESULTS: Drill manoeuvre PF, PLR and PTA were similar, but higher in TRAINED men (PF, PLR: p<0.01; PTA: p<0.05). Peak values in TRAINED men were shown for the halt (mean (SD); PF: 6.5 (1.5) BW; PLR: 983 (333) BW/s PTA; PTA: 207 (57) m/s2) and left turn (PF: 6.6 (1.7) BW; PLR: 928 (300) BW/s; 184 (62) m/s2). Marching PF, PLR, PTA were similar between groups and lower than all drill manoeuvres (PF: 1.1-1.3 BW; PLR: 42-70 BW/s; p<0.01; PTA: 23-38 m/s2; p<0.05). CONCLUSIONS: Army foot drill generates higher forces, loading rates and accelerations than activities such as running and load carriage, while marching is comparable to moderate running (10.8 km/h). The large biomechanical loading of foot drill may contribute to the high rate of overuse injuries during initial military training, and strategies to regulate/reduce this loading should be explored.