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The purpose of this study was firstly to examine the sensitivity of heart rate (HR)‐based and subjective monitoring markers to intensified endurance training; and secondly, to investigate the validity of these markers to distinguish individuals in different fatigue states. A total of 24 recreational runners performed a 3‐week baseline period, a 2‐week overload period, and a 1‐week recovery period. Performance was assessed before and after each period with a 3000m running test. Recovery was monitored with daily orthostatic tests, nocturnal HR recordings, questionnaires, and exercise data. The participants were divided into subgroups (overreached/OR, n = 8; responders/RESP, n = 12) based on the changes in performance and subjective recovery. The responses to the second week of the overload period were compared between the subgroups. RESP improved their baseline 3000 m time (p < 0.001) after the overload period (−2.5 ± 1.0%), and the change differed (p < 0.001) from OR (0.6 ± 1.2%). The changes in nocturnal HR (OR 3.2 ± 3.1%; RESP −2.8 ± 3.7%, p = 0.002) and HR variability (OR −0.7 ± 1.8%; RESP 2.1 ± 1.6%, p = 0.011) differed between the subgroups. In addition, the decrease in subjective readiness to train (p = 0.009) and increase in soreness of the legs (p = 0.04) were greater in OR compared to RESP. Nocturnal HR, readiness to train, and exercise‐derived HR‐running power index had ≥85% positive and negative predictive values in the discrimination between OR and RESP individuals. In conclusion, exercise tolerance can vary substantially in recreational runners. The results supported the usefulness of nocturnal HR and subjective recovery assessments in recognizing fatigue states. Highlights: Tolerance to similarly increased training load varies in recreational runners. While some individuals respond positively, for others the same load may be excessive.Subjective markers, such as readiness to train and soreness of the legs, were the most sensitive markers to respond to increased training load, and the magnitude of these responses was greater in individuals with suspected overreaching.Resting or exercise heart rate (HR) did not respond as systematically as the subjective markers to the training load itself. However, the changes in nocturnal HR, nocturnal HRV, and HR‐running power index started to differ between the RESP and OR subgroups at an earlier stage of the overload period supporting their usefulness as indicators of the fatigue state. [ABSTRACT FROM AUTHOR]

Physically demanding essential military tasks include load carriage, manual material handling and casualty evacuation. This narrative review characterizes the main physical attributes related to performance of these occupational tasks and reviews physical training intervention studies in military settings to improve performance in these military tasks. Load carriage performance requires both aerobic and neuromuscular fitness with greater emphasis on maximal strength and absolute maximal oxygen uptake, especially when carrying heavier loads. In manual material handling, maximal strength and power are strongly associated with discrete lifting, while muscular strength, muscular endurance and aerobic fitness are also associated with repetitive lifting performance. Maximal strength including grip strength, muscular endurance, absolute maximal oxygen uptake and anaerobic capacity are associated with casualty evacuation performance. The results of the present review particularly emphasize the role of muscular fitness in successful performance of the reviewed military occupational tasks. Training intervention studies indicate that load carriage performance can be effectively improved by combining strength, aerobic and specific load carriage training. Improvement in maximal lifting capacity can be achieved by strength training or combined strength and aerobic training, while strength and aerobic training alone, or their combination are effective in improving repetitive lifting, and carry tasks. Only a few studies are available for casualty evacuation and the results are inconclusive but may indicate benefits of strength or combined training. Moreover, emphasis on lower volume but higher intensity in combined training may be a feasible and effective mode to improve military occupational performance in recruits and active-duty soldiers. [ABSTRACT FROM AUTHOR]

This issue of the European Journal of Sport Science includes 8 invited state-of-the-science narrative reviews by well-established researchers in the area of military performance focused on (a) physical training; (b) musculoskeletal injury; (c) adaptive bone formation and stress fracture prevention; (d) sex differences in responses to military stress; (e) load monitoring in military settings; (g) circulating biomarkers related to resilience during military stress; (H) military nutrition research; and (I) development of military exoskeletons. Important historical, current and future scientific and research information and guidance within the context of sustained and improved military physical performance and readiness are provided. Conclusions and recommendations for protecting Soldier health and resiliency include: (1) combined physical training emphasizing higher intensity but lower volume; (2) musculoskeletal injury risk factors most supported from the literature include: female sex, prior injury and low fitness; (3) adequate sleep, vitamin D, calcium, and energy availability are all critical for creating a resilient skeleton protecting against stress fractures; (4) differences between men and women when exposed to military stress include cardiovascular strain, fat oxidation, and psychological health risk; (5) biomarkers (cortisol, epi/norepi, ILs 4, 6, 10, 18 and TNF-alpha, IGF-I, testosterone, DHEA) offer insight for internal stress; (6) monitoring physiological training load should include consideration for multiple inputs, rather than a single measure; (7) nutrition optimization includes determining operational requirements, nutritional practices and nutrient delivery strategies; and (8) future generation exoskeletons will achieve a better balance of intended movement based on individual user and interactions with internal and external constraints. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the effects of two different training programs on strength and power performance and serum hormone concentrations. A total of 104 male soldiers volunteered and took part in the 12‐week training period with baseline, mid‐, and post‐measurements of body composition, muscle strength, lower and upper body power, and blood samples to determine serum hormone concentrations. The mean (±SD) age of subjects was 20 ± 1 years, height 180 ± 6 cm and body mass 72.4 ± 8.8 kg. The subjects were divided into three different training groups: soldier task‐specific training (TS), strength training (ST), and control (CON). Each group had a total of 18 training sessions during the 12‐week study. In the muscle strength tests, most improvements could be observed in the TS and ST groups, especially, during the first weeks of the training period. Maximal isometric leg extension force increased significantly by 7.9 ± 12.2% (p <.05) in the TS and 7.1 ± 12.6% (p <.05) in the ST groups between the PRE and MID, as well as between the PRE and POST measurements by 8.1 ± 12.4% (p <.05) in TS and 12.3 ± 15.3% (p <.01) in ST. Serum TES concentration increased significantly in TS between the PRE and MID (16.8 ± 33.9%) and PRE and POST (11.2 ± 16.7%) measurements. Serum COR concentrations decreased in TS between the MID and POST (−7.8 ± 10.9%) and PRE and POST (−11.0 ± 14.3%) measurements. Although the differences observed were rather minor in magnitude, training in the TS and ST groups led to greater improvements in muscle strength and power performance compared to the training in the CON group. The development of strength and/or power of the lower and upper body was greater in the TS and ST groups, which is crucial for warfighter's performance. Therefore, it is important to have a structured resistance‐training program during military training to optimize the strength, power, and military‐specific performance. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question of the study?What are the effects of caffeine on neuromuscular function in a non‐fatigued state and during fatiguing exercise?What is the main finding and its importance?In a non‐fatigued state, caffeine decreased the duration of the silent period evoked by transcranial magnetic stimulation. Caffeine‐induced reduction of inhibitory mechanisms in the central nervous system before exercise was associated with an increased performance. Individuals who benefit from caffeine ingestion may experience lower perception of effort during exercise and an accelerated recovery of M‐wave amplitude postfatigue. This study elucidates the mechanisms of action of caffeine and demonstrates that inter‐individual variability of its effects on neuromuscular function is a fruitful area for further work. Caffeine enhances exercise performance, but its mechanisms of action remain unclear. In this study, we investigated its effects on neuromuscular function in a non‐fatigued state and during fatiguing exercise. Eighteen men participated in this randomized, double‐blind, placebo‐controlled crossover trial. Baseline measures included plantarflexion force, drop jump, squat jump, voluntary activation of triceps surae muscle, soleus muscle contractile properties, M‐wave, α‐motoneuron excitability (H‐reflex), corticospinal excitability, short‐interval intracortical inhibition, intracortical facilitation, silent period evoked by transcranial magnetic stimulation (SP) and plasma potassium and caffeine concentrations. Immediately after baseline testing, participants ingested caffeine (6 mg·kg−1) or placebo. After a 1‐h rest, baseline measures were repeated, followed by a fatiguing stretch–shortening cycle exercise (sets of 40 bilateral rebound jumps on a sledge apparatus) until task failure. Neuromuscular testing was carried out throughout the fatigue protocol and afterwards. Caffeine enhanced drop jump height (by 4.2%) and decreased the SP (by 12.6%) in a non‐fatigued state. A caffeine‐related decrease in SP and short‐interval intracortical inhibition before the fatiguing activity was associated with an increased time to task failure. The participants who benefitted from an improved performance on the caffeine day reported a significantly lower sense of effort during exercise and had an accelerated postexercise recovery of M‐wave amplitude. Caffeine modulates inhibitory mechanisms of the CNS, recovery of M‐wave amplitude and perception of effort. This study lays the groundwork for future examinations of differences in caffeine‐induced neuromuscular changes between those who are deemed to benefit from caffeine ingestion and those who are not. [ABSTRACT FROM AUTHOR]

Introduction: Physical fitness is strongly related to health and may offer valuable information about public health. We investigated trends in physical fitness, leisure‐time physical activity (LTPA), and anthropometry of young healthy adult Finnish men in representative population‐based samples between 2003 and 2015. Methods: Three independent cross‐sectional samples of 18‐ to 35‐year‐old Finnish men were assessed in 2003 (n = 889), 2008 (n = 803), and 2015 (n = 690). Cardiorespiratory (VO2max) and muscular fitness (1‐minute sit‐ups and push‐ups), body mass, and height were measured. Self‐reported LTPA was assessed. Results: After adjusting for age, education, and smoking, cardiorespiratory fitness was higher in 2003 (mean: 43.5, 95%CI: 42.9‐44.1 mL/kg/min) compared to 2008 (41.3, 95%CI: 40.7‐41.9 mL/kg/min) and 2015 (40.6, 95%CI: 40.0‐41.2 mL/kg/min) (P <.001), whereas no difference was observed between 2008 and 2015. The lowest values in muscular fitness were observed in 2003, while no clear trends were further noticed. The adjusted BMI was higher in 2008 (25.1, 95%CI: 24.9‐25.4) and 2015 (25.3, 95%CI: 25.3, 95%CI: 25.0‐25.6) compared to 2003 (24.5, 95%CI: 24.3‐24.8) (P <.005). In 2015, a higher proportion of individuals exercised at least four times per week compared to 2003 and 2008 (P <.05). Conclusion: The decrease in cardiorespiratory fitness that took place between 2003 and 2008 plateaued after 2008. The plateau is in accordance with the previously observed trend of 5‐10 years younger Finnish men. Moreover, muscular fitness was for the most part higher in 2008 and 2015 compared to 2003. Efforts directed to promote regular physical activity and improve physical fitness are needed. [ABSTRACT FROM AUTHOR]

Abstract: Physical fitness is crucial to warfighters’ performance in the battlefield. Previous studies have shown negative changes in their hormonal and neuromuscular responses induced by military field training (MFT). The purpose of this study was to investigate the changes in hormonal and immunological values and body composition during a prolonged MFT and to find out how warfighters’ physical condition influences these changes. Conscripts (n = 49, age 20 ± 1 years, height 179 ± 9 cm, body mass 73.8 ± 7.8 kg, fat 12.6 ± 3.7% and BMI 23 kg/m²) were measured before, during, after MFT, and after a 4‐day recovery period. Serum insulin‐like growth factor‐1 (IGF‐1), tumor necrosis factor alpha (TNF‐α), interleukin‐6 (IL‐6) concentrations, creatine kinase (CK) activity and leptin concentration were analyzed as well as body composition throughout MFT. Neuromuscular performance was assessed via lower and upper body muscle endurance at the beginning of the study. During MFT, there was a significant decrease (P < 0.05) in body mass (2.3%), fat mass (7.7%) and in muscle mass (2.2%), but all of these values recovered to PRE‐levels after the recovery period. Serum IGF‐1 (22%) and leptin decreased (66%) while CK increased (88%) significantly (P < 0.05) during MFT but recovered at the end of MFT. Upper body dynamic and trunk isometric muscular endurance had a positive correlation (r = 0.37. P < 0.05) with the change in IGF‐1 during MFT and a negative correlation with the changes in CK (−0.34, P < 0.05). The results show that there were negative changes in conscript's body composition and hormonal and immunological values during the prolonged MFT. These changes suggest that the physiological stress was high during MFT. High levels of upper body and trunk muscular strength were negatively correlated with warfighters’ physiological effects and should therefore be developed prior to actual deployment to reduce the physical decline experienced during prolonged MFTs. [ABSTRACT FROM AUTHOR]

Abstract: An exercise bout or a dehydration often causes a reduction in plasma volume, which should be acknowledged when considering the change in biomarkers before and after the plasma changing event. The classic equation from Dill and Costill (1974, J. Appl. Physiol., 37, 247–248) for plasma volume shift is usually utilized in such a case. Although this works well with plasma and serum biomarkers, we argue in this note that this traditional approach gives misleading results in the context of whole blood biomarkers, such as lactate, white cells, and thrombocytes. In this study, we demonstrate that to calculate the change in the total amount of circulating whole blood biomarker, one should utilize a formula BM post BM pre × H b pre H b post − 1 . Here Hb and BM are, respectively, the concentrations for the hemoglobin and for the inspected whole blood biomarker before (pre) and after (post) the plasma changing incident. [ABSTRACT FROM AUTHOR]

The primary aim of the present study was to investigate the acute gene expression responses of PGC-1 isoforms and PGC-1α target genes related to mitochondrial biogenesis ( cytochrome C), angiogenesis ( VEGF-A), and muscle hypertrophy (myostatin), after a resistance or endurance exercise bout. In addition, the study aimed to elucidate whether the expression changes of studied transcripts were linked to phosphorylation of AMPK and MAPK p38. Nineteen physically active men were divided into resistance exercise ( RE, n = 11) and endurance exercise ( EE, n = 8) groups. RE group performed leg press exercise (10 × 10 RM, 50 min) and EE walked on a treadmill (~80% HRmax, 50 min). Muscle biopsies were obtained from the vastus lateralis muscle before, 30 min, and 180 min after exercise. EE and RE significantly increased the gene expression of alternative promoter originated PGC-1α exon 1b- and 1bxs'-derived isoforms, whereas the proximal promoter originated exon 1a-derived transcripts were less inducible and were upregulated only after EE. Truncated PGC-1α transcripts were upregulated both after EE and RE. Neither RE nor EE affected the expression of PGC-1β. EE upregulated the expression of cytochrome C and VEGF-A, whereas RE upregulated VEGF-A and downregulated myostatin. Both EE and RE increased the levels of p- AMPK and p- MAPK p38, but these changes were not linked to the gene expression responses of PGC-1 isoforms. The present study comprehensively assayed PGC-1 transcripts in human skeletal muscle and showed exercise mode-specific responses thus improving the understanding of early signaling events in exercise-induced muscle adaptations. [ABSTRACT FROM AUTHOR]

Sleep is the most important period for recovery from daily load. Regular physical activity enhances overall sleep quality, but the effects of acute exercise on sleep are not well defined. In sleep hygiene recommendations, intensive exercising is not suggested within the last 3 h before bed time, but this recommendation has not been adequately tested experimentally. Therefore, the effects of vigorous late-night exercise on sleep were examined by measuring polysomnographic, actigraphic and subjective sleep quality, as well as cardiac autonomic activity. Eleven (seven men, four women) physically fit young adults (VO 54 ± 8 mL·kg·min, age 26 ± 3 years) were monitored in a sleep laboratory twice in a counterbalanced order: (1) after vigorous late-night exercise; and (2) after a control day without exercise. The incremental cycle ergometer exercise until voluntary exhaustion started at 21:00 ± 00:28 hours, lasted for 35 ± 3 min, and ended 2:13 ± 00:19 hours before bed time. The proportion of non-rapid eye movement sleep was greater after the exercise day than the control day ( P < 0.01), while no differences were seen in actigraphic or subjective sleep quality. During the whole sleep, no differences were found in heart rate (HR) variability, whereas HR was higher after the exercise day than the control day (54 ± 7 versus 51 ± 7, P < 0.01), and especially during the first three sleeping hours. The results indicate that vigorous late-night exercise does not disturb sleep quality. However, it may have effects on cardiac autonomic control of heart during the first sleeping hours. [ABSTRACT FROM AUTHOR]

The association between muscle oxygen uptake (VO2) and perfusion or perfusion heterogeneity (relative dispersion, RD) was studied in eight healthy male subjects during intermittent isometric (1 s on, 2 s off) one-legged knee-extension exercise at variable intensities using positron emission tomography and a-v blood sampling. Resistance during the first 6 min of exercise was 50% of maximal isometric voluntary contraction force (MVC) (HI-1), followed by 6 min at 10% MVC (LOW) and finishing with 6 min at 50% MVC (HI-2). Muscle perfusion and O2 delivery during HI-1 (26 ± 5 and 5·4 ± 1·0 ml 100 g−1 min−1) and HI-2 (28 ± 4 and 5·8 ± 0·7 ml 100 g−1 min−1) were similar, but both were higher ( P<0·01) than during LOW (15 ± 3 and 3·0 ± 0·6 ml 100 g−1 min−1). Muscle VO2 was also higher during both HI workloads (HI-1 3·3 ± 0·4 and HI-2 4·1 ± 0·6 ml 100 g−1 min−1) than LOW (1·4 ± 0·4 ml 100 g−1 min−1; P<0·01) and 25% higher during HI-2 than HI-1 ( P<0·05). O2 extraction was higher during HI workloads (HI-1 62 ± 7 and HI-2 70 ± 7%) than LOW (45 ± 8%; P<0·01). O2 extraction tended to be higher ( P = 0·08) during HI-2 when compared to HI-1. Perfusion was less heterogeneous ( P<0·05) during HI workloads when compared to LOW with no difference between HI workloads. Thus, during one-legged knee-extension exercise at variable intensities, skeletal muscle perfusion and O2 delivery are unchanged between high-intensity workloads, whereas muscle VO2 is increased during the second high-intensity workload. Perfusion heterogeneity cannot explain this discrepancy between O2 delivery and uptake. We propose that the excess muscle VO2 during the second high-intensity workload is derived from working muscle cells. [ABSTRACT FROM AUTHOR]

Leptin regulates body weight, metabolism, and tissue adaptations to environmental stressors. We examined the association of single nucleotide polymorphism (SNP) of leptin promoter G-2548A (rs7799039) and leptin receptor Gln223Arg (rs1137101) with body composition, plasma leptin levels, and peak oxygen uptake (VO2peak) in response to 8 weeks of physical training in 48 male military conscripts. AA homozygotes of leptin promoter SNP-2548 showed higher body fat and BMI values than G allele carriers. Acute exercise decreased leptin levels in G allele carriers, but increased in AA homozygotes. Physical training significantly decreased BMI values and also a tendency for decreased plasma leptin levels was observed in all subjects. In G allele carriers, BMI loss was mainly due to decreased fat mass, whereas in AA homozygotes due to loss of fat-free mass. Training increased VO2peak in all subjects with most prominent effects in G allele carriers. Regarding leptin receptor SNP, there were no statistically significant differences in BMI values between the genotype groups at baseline or after physical training. Our results suggest that physical training-induced alterations in body composition and plasma leptin may be influenced by a genetic variation of leptin promoter but not of leptin receptor. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The relationships between electromyographic (EMG) activity and force as well as muscle blood flow and work have been well established. However, the association between muscle blood flow and EMG activity remains unsolved. Thus, to test the hypothesis that muscle EMG activity relates to muscle perfusion in different compartments of the quadriceps femoris (QF) muscle, 12 healthy male subjects were studied. During two very submaximal exercise bouts, at different exercise intensities, oxygen labelled radiowater and positron emission tomography were used to measure muscle perfusion. In addition, produced force of knee extensors and muscle EMG activity in the vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles were recorded during both exercise bouts. Although the exercise intensity and average force production was higher during the second exercise bout (38 ± 15 versus 51 ± 17 N; P = 0·007), the mean EMG activity was lower (RF; P<0·001) or unchanged (VL; P = 0·722 and VM; P = 0·640). During the second exercise period, perfusion also remained unchanged in the entire QF muscle ( P = 0·223) and in its separate muscles (VL, P = 0·703; VM, P = 0·141; RF, P = 0·113) in a group level. However, the individual changes in muscle perfusion were tightly related to changes in muscle EMG activity in VL ( r = 0·84; P = 0·002) and VM ( r = 0·68; P = 0·015) but poorly in the RF muscle ( r = 0·40; P = 0·257). In conclusion, the different associations between muscle perfusion and EMG activity in different QF muscles suggests specific functional role of the vasti muscles and the RF muscle. [ABSTRACT FROM AUTHOR]

Forward pulled running on a treadmill is known to increase mechanical and decrease metabolic constrains relative to normal running. This experimental situation was used to investigate the variations of the mechanical parameters induced by the pulling. Ten subjects ran during 3 min at individually predetermined constant speeds of 16.4 ± 1.4 km ⋅ h[sup-1] on a treadmill while being forward pulled by a load equal to 5% of their body weight. Ground reaction forces were recorded during the last 30 s of the run. Kinematic parameters of the stride as well as impulses and mechanical work were then calculated. Stride frequency did not change, while horizontal impulses were highly modified (+38% and -28%, respectively, for the braking and pushing impulses). Simultaneously, external work produced during the braking and pushing phases was modified by +6.5% and -4.7%, respectively. Therefore, the horizontal impulses were far more modified than the mechanical work. As a consequence, the estimation of the relative influence of negative (braking) and positive (push-off) phases on metabolic cost of running could be quite different when forces, impulses, or work are considered. [ABSTRACT FROM AUTHOR]