Showing papers in "European Journal of Applied Physiology in 2021"

Low energy availability: history, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males

Abstract: Energy availability (EA) is defined as the amount of dietary energy available to sustain physiological function after subtracting the energetic cost of exercise. Insufficient EA due to increased exercise, reduced energy intake, or a combination of both, is a potent disruptor of the endocrine milieu. As such, EA is conceived as a key etiological factor underlying a plethora of physiological dysregulations described in the female athlete triad, its male counterpart and the Relative Energy Deficiency in Sport models. Originally developed upon female-specific physiological responses, this concept has recently been extended to males, where experimental evidence is limited. The majority of data for all these models are from cross-sectional or observational studies where hypothesized chronic low energy availability (LEA) is linked to physiological maladaptation. However, the body of evidence determining causal effects of LEA on endocrine, and physiological function through prospective studies manipulating EA is comparatively small, with interventions typically lasting ≤ 5 days. Extending laboratory-based findings to the field requires recognition of the strengths and limitations of current knowledge. To aid this, this review will: (1) provide a brief historical overview of the origin of the concept in mammalian ecology through its evolution of algebraic calculations used in humans today, (2) Outline key differences from the ‘energy balance’ concept, (3) summarise and critically evaluate the effects of LEA on tissues/systems for which we now have evidence, namely: hormonal milieu, reproductive system endocrinology, bone metabolism and skeletal muscle; and finally (4) provide perspectives and suggestions for research upon identified knowledge gaps.

Echo intensity as an indicator of skeletal muscle quality: applications, methodology, and future directions.

Abstract: This narrative review provides an overview of the current knowledge of B-mode ultrasound-derived echo intensity (EI) as an indicator of skeletal muscle quality. PubMed and Google Scholar were used to search the literature. Advanced search functions were used to find original studies with the terms ‘echo intensity’ and/or ‘muscle quality’ in the title and/or abstract. Publications that conceptually described muscle quality but did not include measurement of EI were not a focus of the review. Importantly, the foundational premise of EI remains unclear. While it is likely that EI reflects intramuscular adiposity, data suggesting that these measurements are influenced by fibrous tissue is limited to diseased muscle and animal models. EI appears to show particular promise in studying muscular aging. Studies have consistently reported an association between EI and muscle function, though not all chronic interventions have demonstrated improvements. Based on the existing literature, it is unclear if EI can be used as a marker of muscle glycogen following exercise and nutritional interventions, or if EI is influenced by hydration status. Inconsistent methodological approaches used across laboratories have made comparing EI studies challenging. Image depth, rest duration, participant positioning, probe tilt, and the decision to correct for subcutaneous adipose tissue thickness are all critical considerations when interpreting the literature and planning studies. While some areas show conflicting evidence, EI shows promise as a novel tool for studying muscle quality. Collaborative efforts focused on methodology are necessary to enhance the consistency and quality of the EI literature.

The knowns and unknowns of neural adaptations to resistance training.

Abstract: The initial increases in force production with resistance training are thought to be primarily underpinned by neural adaptations. This notion is firmly supported by evidence displaying motor unit adaptations following resistance training; however, the precise locus of neural adaptation remains elusive. The purpose of this review is to clarify and critically discuss the literature concerning the site(s) of putative neural adaptations to short-term resistance training. The proliferation of studies employing non-invasive stimulation techniques to investigate evoked responses have yielded variable results, but generally support the notion that resistance training alters intracortical inhibition. Nevertheless, methodological inconsistencies and the limitations of techniques, e.g. limited relation to behavioural outcomes and the inability to measure volitional muscle activity, preclude firm conclusions. Much of the literature has focused on the corticospinal tract; however, preliminary research in non-human primates suggests reticulospinal tract is a potential substrate for neural adaptations to resistance training, though human data is lacking due to methodological constraints. Recent advances in technology have provided substantial evidence of adaptations within a large motor unit population following resistance training. However, their activity represents the transformation of afferent and efferent inputs, making it challenging to establish the source of adaptation. Whilst much has been learned about the nature of neural adaptations to resistance training, the puzzle remains to be solved. Additional analyses of motoneuron firing during different training regimes or coupling with other methodologies (e.g., electroencephalography) may facilitate the estimation of the site(s) of neural adaptations to resistance training in the future.

Mechanisms underlying performance impairments following prolonged static stretching without a comprehensive warm-up

Abstract: Whereas a variety of pre-exercise activities have been incorporated as part of a “warm-up” prior to work, combat, and athletic activities for millennia, the inclusion of static stretching (SS) within a warm-up has lost favor in the last 25 years. Research emphasized the possibility of SS-induced impairments in subsequent performance following prolonged stretching without proper dynamic warm-up activities. Proposed mechanisms underlying stretch-induced deficits include both neural (i.e., decreased voluntary activation, persistent inward current effects on motoneuron excitability) and morphological (i.e., changes in the force–length relationship, decreased Ca2+ sensitivity, alterations in parallel elastic component) factors. Psychological influences such as a mental energy deficit and nocebo effects could also adversely affect performance. However, significant practical limitations exist within published studies, e.g., long-stretching durations, stretching exercises with little task specificity, lack of warm-up before/after stretching, testing performed immediately after stretch completion, and risk of investigator and participant bias. Recent research indicates that appropriate durations of static stretching performed within a full warm-up (i.e., aerobic activities before and task-specific dynamic stretching and intense physical activities after SS) have trivial effects on subsequent performance with some evidence of improved force output at longer muscle lengths. For conditions in which muscular force production is compromised by stretching, knowledge of the underlying mechanisms would aid development of mitigation strategies. However, these mechanisms are yet to be perfectly defined. More information is needed to better understand both the warm-up components and mechanisms that contribute to performance enhancements or impairments when SS is incorporated within a pre-activity warm-up.

Exercise-induced muscle damage: mechanism, assessment and nutritional factors to accelerate recovery.

Abstract: There have been a multitude of reviews written on exercise-induced muscle damage (EIMD) and recovery. EIMD is a complex area of study as there are a host of factors such as sex, age, nutrition, fitness level, genetics and familiarity with exercise task, which influence the magnitude of performance decrement and the time course of recovery following EIMD. In addition, many reviews on recovery from exercise have ranged from the impact of nutritional strategies and recovery modalities, to complex mechanistic examination of various immune and endocrine signaling molecules. No one review can adequately address this broad array of study. Thus, in this present review, we aim to examine EIMD emanating from both endurance exercise and resistance exercise training in recreational and competitive athletes and shed light on nutritional strategies that can enhance and accelerate recovery following EIMD. In addition, the evaluation of EIMD and recovery from exercise is often complicated and conclusions often depend of the specific mode of assessment. As such, the focus of this review is also directed at the available techniques used to assess EIMD.

How to improve the muscle synergy analysis methodology

Abstract: Muscle synergy analysis is increasingly used in domains such as neurosciences, robotics, rehabilitation or sport sciences to analyze and better understand motor coordination. The analysis uses dimensionality reduction techniques to identify regularities in spatial, temporal or spatio-temporal patterns of multiple muscle activation. Recent studies have pointed out variability in outcomes associated with the different methodological options available and there was a need to clarify several aspects of the analysis methodology. While synergy analysis appears to be a robust technique, it remain a statistical tool and is, therefore, sensitive to the amount and quality of input data (EMGs). In particular, attention should be paid to EMG amplitude normalization, baseline noise removal or EMG filtering which may diminish or increase the signal-to-noise ratio of the EMG signal and could have major effects on synergy estimates. In order to robustly identify synergies, experiments should be performed so that the groups of muscles that would potentially form a synergy are activated with a sufficient level of activity, ensuring that the synergy subspace is fully explored. The concurrent use of various synergy formulations-spatial, temporal and spatio-temporal synergies- should be encouraged. The number of synergies represents either the dimension of the spatial structure or the number of independent temporal patterns, and we observed that these two aspects are often mixed in the analysis. To select a number, criteria based on noise estimates, reliability of analysis results, or functional outcomes of the synergies provide interesting substitutes to criteria solely based on variance thresholds.

A comparison of foam rolling and vibration foam rolling on the quadriceps muscle function and mechanical properties

Abstract: The purpose of the study was to investigate the effects of using a vibration foam roll (VFR) or a non-vibration foam roll (NVFR) on maximum voluntary isometric contraction peak torque (MVIC), range of motion (ROM), passive resistive torque (PRT), and shear modulus. Twenty-one male volunteers visited the laboratory on two separate days and were randomly assigned to either a VFR group or a NVFR group. Both interventions were performed for 3 × 1 min each. Before and after each intervention, passive resistive torque and maximum voluntary isometric contraction peak torque of the leg extensors were assessed with a dynamometer. Hip extension ROM was assessed using a modified Thomas test with 3D-motion caption. Muscle shear modulus of the vastus lateralis (VL), vastus medialis (VM), and rectus femoris (RF) was assessed with shear wave elastography (SWE). In both groups (VFR, NVFR) we observed an increase in MVIC peak torque (+ 14.2 Nm, + 8.6 Nm) and a decrease in shear modulus of the RF (− 7.2 kPa, − 4.7 kPa). However, an increase in hip extension ROM (3.3°) was only observed in the VFR group. There was no change in PRT and shear modulus of the VL and VM, in both the VFR group and the NVFR group. Our findings demonstrate a muscle-specific acute decrease in passive RF stiffness after VFR and NVFR, with an effect on joint flexibility found only after VFR. The findings of this study suggest that VFR might be a more efficient approach to maximize performance in sports with flexibility demands.

Transferring clinically established immune inflammation markers into exercise physiology: focus on neutrophil-to-lymphocyte ratio, platelet-to-lymphocyte ratio and systemic immune-inflammation index

Abstract: Over the last decades the cellular immune inflammation markers neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR) and systemic immune-inflammation index (SII = NLR × platelets) have emerged in clinical context as markers of disease-related inflammation and are now widely appreciated due to their integrative character. Transferring these clinically established inflammation markers into exercise physiology seems highly beneficial, especially due to the low temporal, financial and infrastructural resources needed for assessment and calculation. Therefore, the aim of this review is to summarize evidence on the value of the integrative inflammation markers NLR, PLR and SII for depiction of exercise-induced inflammation and highlight potential applications in exercise settings. Despite sparse evidence, multiple investigations revealed responsiveness of the markers to acute and chronic exercise, thereby opening promising avenues in the field of exercise physiology. In performance settings, they might help to infer information for exercise programming by reflecting exercise strain and recovery status or periods of overtraining and increased infection risk. In health settings, application involves the depiction of anti-inflammatory effects of chronic exercise in patients exhibiting chronic inflammation. Further research should, therefore, focus on establishing reference values for these integrative markers in athletes at rest, assess the kinetics and reliability in response to different exercise modalities and implement the markers into clinical exercise trials to depict anti-inflammatory effects of chronic exercise in different patient collectives.

Body mapping of regional sweat distribution in young and older males

Abstract: Given the pressing impact of global warming and its detrimental effect on the health of older populations, understanding age-related changes in thermoregulatory function is essential. Age differences in regional sweat distribution have been observed previously, but given the typically small measurement areas assessed, the development of whole body sweat maps for older individuals is required. Therefore, this study investigated age-related differences in regional sweat distribution in a hot environment (32 °C/50%RH) in young and older adults, using a body mapping approach. Technical absorbent pads were applied to the skin of 14 young (age 24 ± 2 years) and 14 older (68 ± 5 years) males to measure regional sweat rate (RSR) at rest (30 min) and during exercise (30 min), at a fixed heat production (200 W m−2). Gastrointestinal (Tgi) and skin temperature (Tsk), heart rate, thermal sensation, and thermal comfort were also measured. Whole body sweat maps showed that despite equal heat production, healthy older males had significantly lower gross sweat loss (GSL) than the young and significantly lower RSR at almost all body regions at rest and at the hands, legs, ankles, and feet during exercise. The lower sweat loss in the older group coincided with a greater increase in Tgi and a consistently higher Tsk at the legs, despite subjectively feeling slightly cooler than younger individuals. These findings support the evidence of age-related deterioration in both autonomic and subjective responses in the heat and highlight the lower extremities as the most affected body region.

Effects of a high-volume static stretching programme on plantar-flexor muscle strength and architecture.

Abstract: Static stretching (SS) is performed in various settings, but there is no consensus about the effects of SS programmes on changes in muscle morphofunction. This study aimed to investigate the effects of a high-volume SS programme on muscle strength and architecture. Sixteen healthy young male adults participated, and the dominant leg was defined as the intervention side, with the non-dominant leg as the control side. Stretching exercises were performed two times per week (6 sets of 5 min, totally 30 min per session,) for 5-week using a stretching board under the supervision of the research team. Before and after SS intervention programme, plantar-flexor strength (maximum voluntary isometric contraction, MVC-ISO; maximum voluntary concentric contraction, MVC-CON) and architecture (muscle thickness, pennation angle, and fascicle length) were measured via dynamometer and ultrasound, respectively. Following the SS-training programme, significant increases were observed for stretching side in MVIC-ISO at neutral ankle position (p = 0.02, d = 0.31, Δ = 6.4 ± 9.9%) and MVC-CON at 120°/s (p = 0.02, d = 0.30, Δ = 7.8 ± 9.1%), with no significant change on the control side. There was no significant change in any measure of muscle architecture for both intervention and control sides. Five-week high-volume SS induced positive changes on some measures of muscle strength but not hypertrophy of plantar-flexor muscles. Even with a volume much greater than already tested, the low strain offered by the SS per set seems be insufficient to induce architectural changes on skeletal muscle.

Power profiling and the power-duration relationship in cycling: a narrative review.

Abstract: Emerging trends in technological innovations, data analysis and practical applications have facilitated the measurement of cycling power output in the field, leading to improvements in training prescription, performance testing and race analysis. This review aimed to critically reflect on power profiling strategies in association with the power-duration relationship in cycling, to provide an updated view for applied researchers and practitioners. The authors elaborate on measuring power output followed by an outline of the methodological approaches to power profiling. Moreover, the deriving a power-duration relationship section presents existing concepts of power-duration models alongside exercise intensity domains. Combining laboratory and field testing discusses how traditional laboratory and field testing can be combined to inform and individualize the power profiling approach. Deriving the parameters of power-duration modelling suggests how these measures can be obtained from laboratory and field testing, including criteria for ensuring a high ecological validity (e.g. rider specialization, race demands). It is recommended that field testing should always be conducted in accordance with pre-established guidelines from the existing literature (e.g. set number of prediction trials, inter-trial recovery, road gradient and data analysis). It is also recommended to avoid single effort prediction trials, such as functional threshold power. Power-duration parameter estimates can be derived from the 2 parameter linear or non-linear critical power model: P(t) = W′/t + CP (W′—work capacity above CP; t—time). Structured field testing should be included to obtain an accurate fingerprint of a cyclist’s power profile.

Regulation of muscle potassium: exercise performance, fatigue and health implications.

Abstract: This review integrates from the single muscle fibre to exercising human the current understanding of the role of skeletal muscle for whole-body potassium (K+) regulation, and specifically the regulation of skeletal muscle [K+]. We describe the K+ transport proteins in skeletal muscle and how they contribute to, or modulate, K+ disturbances during exercise. Muscle and plasma K+ balance are markedly altered during and after high-intensity dynamic exercise (including sports), static contractions and ischaemia, which have implications for skeletal and cardiac muscle contractile performance. Moderate elevations of plasma and interstitial [K+] during exercise have beneficial effects on multiple physiological systems. Severe reductions of the trans-sarcolemmal K+ gradient likely contributes to muscle and whole-body fatigue, i.e. impaired exercise performance. Chronic or acute changes of arterial plasma [K+] (hyperkalaemia or hypokalaemia) have dangerous health implications for cardiac function. The current mechanisms to explain how raised extracellular [K+] impairs cardiac and skeletal muscle function are discussed, along with the latest cell physiology research explaining how calcium, β-adrenergic agonists, insulin or glucose act as clinical treatments for hyperkalaemia to protect the heart and skeletal muscle in vivo. Finally, whether these agents can also modulate K+-induced muscle fatigue are evaluated.

Chronic resistance training: is it time to rethink the time course of neural contributions to strength gain?

Abstract: Resistance training enhances muscular force due to a combination of neural plasticity and muscle hypertrophy It has been well documented that the increase in strength over the first few weeks of resistance training (ie acute) has a strong underlying neural component and further enhancement in strength with long-term (ie chronic) resistance training is due to muscle hypertrophy For obvious reasons, collecting long-term data on how chronic-resistance training affects the nervous system not feasible As a result, the effect of chronic-resistance training on neural plasticity is less understood and has not received systematic exploration Thus, the aim of this review is to provide rationale for investigating neural plasticity beyond acute-resistance training We use cross-sectional work to highlight neural plasticity that occurs with chronic-resistance training at sites from the brain to spinal cord Specifically, intra-cortical circuitry and the spinal motoneuron seem to be key sites for this plasticity We then urge the need to further investigate the differential effects of acute versus chronic-resistance training on neural plasticity, and the role of this plasticity in increased strength Such investigations may help in providing a clearer definition of the continuum of acute and chronic-resistance training, how the nervous system is altered during this continuum and the causative role of neural plasticity in changes in strength over the continuum of resistance training

Physiology, pathophysiology and (mal)adaptations to chronic apnoeic training: a state-of-the-art review

Abstract: Breath-hold diving is an activity that humans have engaged in since antiquity to forage for resources, provide sustenance and to support military campaigns. In modern times, breath-hold diving continues to gain popularity and recognition as both a competitive and recreational sport. The continued progression of world records is somewhat remarkable, particularly given the extreme hypoxaemic and hypercapnic conditions, and hydrostatic pressures these athletes endure. However, there is abundant literature to suggest a large inter-individual variation in the apnoeic capabilities that is thus far not fully understood. In this review, we explore developments in apnoea physiology and delineate the traits and mechanisms that potentially underpin this variation. In addition, we sought to highlight the physiological (mal)adaptations associated with consistent breath-hold training. Breath-hold divers (BHDs) are evidenced to exhibit a more pronounced diving-response than non-divers, while elite BHDs (EBHDs) also display beneficial adaptations in both blood and skeletal muscle. Importantly, these physiological characteristics are documented to be primarily influenced by training-induced stimuli. BHDs are exposed to unique physiological and environmental stressors, and as such possess an ability to withstand acute cerebrovascular and neuronal strains. Whether these characteristics are also a result of training-induced adaptations or genetic predisposition is less certain. Although the long-term effects of regular breath-hold diving activity are yet to be holistically established, preliminary evidence has posed considerations for cognitive, neurological, renal and bone health in BHDs. These areas should be explored further in longitudinal studies to more confidently ascertain the long-term health implications of extreme breath-holding activity.

Effects of acute and sub-acute hypobaric hypoxia on oxidative stress: a field study in the Alps

Abstract: High altitude results in lower barometric pressure and hence partial pressure of O2 decrease can lead to several molecular and cellular changes, such as generation of reactive oxygen species (ROS). Electron Paramagnetic Resonance technique was adopted in the field, to evaluate the effects of acute and sub-acute hypobaric hypoxia (HH) on ROS production by micro-invasive method. Biological biomarkers, indicators of oxidative stress, renal function and inflammation were investigated too. Fourteen lowlander subjects (mean age 27.3 ± 5.9 years) were exposed to HH at 3269 m s.l. ROS production, related oxidative damage to cellular components, systemic inflammatory response and renal function were determined through blood and urine profile performed at 1st, 2nd, 4th, 7th, and 14th days during sojourn. Kinetics of changes during HH exposition showed out significant (range p < 0.05–0.0001) increases that at max corresponds to 38% for ROS production rate, 140% for protein carbonyl, 44% for lipid peroxidation, 42% for DNA damage, 200% for inflammatory cytokines and modifications in renal function (assessed by neopterin concentration: 48%). Conversely, antioxidant capacity significantly (p < 0.0001) decreased − 17% at max. This 14 days in-field study describes changes of oxidative-stress biomarkers during HH exposure in lowlanders. The results show an overproduction of ROS and consequent oxidative damage to protein, lipids and DNA with a decrease in antioxidant capacity and the involvement of inflammatory status and a transient renal dysfunction. Exposure at high altitude induces a hypoxic condition during acute and sub-acute phases accompanied by molecular adaptation mechanism indicating acclimatization.

The (in)dependency of blood and sweat sodium, chloride, potassium, ammonia, lactate and glucose concentrations during submaximal exercise

Abstract: To reduce the need for invasive and expensive measures of human biomarkers, sweat is becoming increasingly popular in use as an alternative to blood. Therefore, the (in)dependency of blood and sweat composition has to be explored. In an environmental chamber (33 °C, 65% relative humidity; RH), 12 participants completed three subsequent 20-min cycling stages to elicit three different local sweat rates (LSR) while aiming to limit changes in blood composition: at 60% of their maximum heart rate (HRmax), 70% HRmax and 80% HRmax, with 5 min of seated-rest in between. Sweat was collected from the arm and back during each stage and post-exercise. Blood was drawn from a superficial antecubital vein in the middle of each stage. Concentrations of sodium, chloride, potassium, ammonia, lactate and glucose were determined in blood plasma and sweat. With increasing exercise intensity, LSR, sweat sodium, chloride and glucose concentrations increased (P ≤ 0.026), while simultaneously limited changes in blood composition were elicited for these components (P ≥ 0.093). Sweat potassium, lactate and ammonia concentrations decreased (P ≤ 0.006), while blood potassium decreased (P = 0.003), and blood ammonia and lactate concentrations increased with higher exercise intensities (P = 0.005; P = 0.007, respectively). The vast majority of correlations between blood and sweat parameters were non-significant (P > 0.05), with few exceptions. The data suggest that sweat composition is at least partly independent of blood composition. This has important consequences when targeting sweat as non-invasive alternative for blood measurements.

The effects of 12 weeks of static stretch training on the functional, mechanical, and architectural characteristics of the triceps surae muscle-tendon complex.

Abstract: We investigated the effects of 12 weeks of passive static stretching training (PST) on force-generating capacity, passive stiffness, muscle architecture of plantarflexor muscles. Thirty healthy adults participated in the study. Fifteen participants (STR, 6 women, 9 men) underwent 12-week plantarflexor muscles PST [(5 × 45 s-on/15 s-off) × 2exercises] × 5times/week (duration: 2250 s/week), while 15 participants (CTRL, 6 women, 9 men) served as control (no PST). Range of motion (ROM), maximum passive resistive torque (PRTmax), triceps surae architecture [fascicle length, fascicle angle, and thickness], passive stiffness [muscle–tendon complex (MTC) and muscle stiffness], and plantarflexors maximun force-generating capacity variables (maximum voluntary contraction, maximum muscle activation, rate of torque development, electromechanical delay) were calculated Pre, at the 6th (Wk6), and the 12th week (Wk12) of the protocol in both groups. Compared to Pre, STR ROM increased (P 0.05). Percentage changes in ROM correlated with percentage changes in PRTmax (ρ = 0.62, P = 0.01) and MTC stiffness (ρ = − 0.78, P = 0.001). In CTRL, no changes (P > 0.05) occurred in any variables at any time point. The expected long-term PST-induced changes in ROM were associated with modifications in the whole passive mechanical properties of the ankle joint, while maximum force-generating capacity characteristics were preserved. 12 weeks of PST do not seem a sufficient stimulus to induce triceps surae architectural changes.

Fatigue development and perceived response during self-paced endurance exercise: state-of-the-art review

Abstract: Performance in self-paced endurance exercises results from continuous fatigue symptom management. While it is suggested that perceived responses and neuromuscular fatigue development may determine variations in exercise intensity, it is uncertain how these fatigue components interact throughout the task. To address the fatigue development in self-paced endurance exercises, the following topics were addressed in the present review: (1) fatigue development during constant-load vs. self-paced endurance exercises; (2) central and peripheral fatigue and perceived exertion interconnections throughout the self-paced endurance exercises; and (3) future directions and recommendations. Based on the available literature, it is suggested (1) the work rate variations during a self-paced endurance exercise result in transitions between exercise intensity domains, directly impacting the end-exercise central and peripheral fatigue level when compared to constant-load exercise mode; (2) central and peripheral fatigue, as well as perceived exertion response contribute to exercise intensity regulation at the different stages of the trial. It seems that while neuromuscular fatigue development might be relevant at beginning of the trial, the perceived exertion might interfere in the remaining parts to achieve maximal values only at the finish line; (3) future studies should focus on the mechanisms underpinning fatigue components interactions throughout the task and its influence on exercise intensity variations.

The contemporary model of vertebral column joint dysfunction and impact of high-velocity, low-amplitude controlled vertebral thrusts on neuromuscular function

Abstract: There is growing evidence that vertebral column function and dysfunction play a vital role in neuromuscular control. This invited review summarises the evidence about how vertebral column dysfunction, known as a central segmental motor control (CSMC) problem, alters neuromuscular function and how spinal adjustments (high-velocity, low-amplitude or HVLA thrusts directed at a CSMC problem) and spinal manipulation (HVLA thrusts directed at segments of the vertebral column that may not have clinical indicators of a CSMC problem) alters neuromuscular function. The current review elucidates the peripheral mechanisms by which CSMC problems, the spinal adjustment or spinal manipulation alter the afferent input from the paravertebral tissues. It summarises the contemporary model that provides a biologically plausible explanation for CSMC problems, the manipulable spinal lesion. This review also summarises the contemporary, biologically plausible understanding about how spinal adjustments enable more efficient production of muscular force. The evidence showing how spinal dysfunction, spinal manipulation and spinal adjustments alter central multimodal integration and motor control centres will be covered in a second invited review. Many studies have shown spinal adjustments increase voluntary force and prevent fatigue, which mainly occurs due to altered supraspinal excitability and multimodal integration. The literature suggests physical injury, pain, inflammation, and acute or chronic physiological or psychological stress can alter the vertebral column’s central neural motor control, leading to a CSMC problem. The many gaps in the literature have been identified, along with suggestions for future studies. Spinal adjustments of CSMC problems impact motor control in a variety of ways. These include increasing muscle force and preventing fatigue. These changes in neuromuscular function most likely occur due to changes in supraspinal excitability. The current contemporary model of the CSMC problem, and our understanding of the mechanisms of spinal adjustments, provide a biologically plausible explanation for how the vertebral column’s central neural motor control can dysfunction, can lead to a self-perpetuating central segmental motor control problem, and how HVLA spinal adjustments can improve neuromuscular function.

HIIT is superior than MICT on cardiometabolic health during training and detraining

Abstract: This study investigated the cardiometabolic health of overweight/obese untrained individuals in response to 8 weeks of HIIT and MICT using a field approach, and to 4 weeks of training cessation (TC). Twenty-two subjects performed 8 weeks of moderate intensity continuous training (MICT—n = 11) or high-intensity interval training (HIIT—n = 11) (outdoor running), followed by 4 weeks of TC. Cardiorespiratory fitness, body composition, arterial blood pressure, glucose metabolism and blood lipids were measured pre-training (PRE), post-training (POST) and TC. HIIT improved eight indicators of cardiometabolic health ( $$V{\text{O}}_{2\max }$$ , BMI, body fat, visceral fat, systolic blood pressure, total cholesterol, fasting glucose and triglycerides—p < 0.05) while MICT only three ( $$V{\text{O}}_{2\max }$$ , BMI, and visceral fat—p < 0.05). After 4 weeks of TC, four positive adaptations from HIIT were negatively affected ( $$V{\text{O}}_{2\max }$$ , visceral fat, systolic blood pressure and total cholesterol—p < 0.05) and three in the MICT group ( $$V{\text{O}}_{2\max }$$ , BMI and visceral fat, p < 0.05). Eight weeks of HIIT performed in a real-world setting promoted a greater number of positive adaptations in cardiometabolic health of individuals with overweight/obese compared to MICT. Most of the positive effects of the HIIT protocol were also found to be longer lasting and maintained after the suspension of high-intensity interval running for 4 weeks. Conversely, all positive effects of MICT protocols were reversed after TC.

Novel insights on caffeine supplementation, CYP1A2 genotype, physiological responses and exercise performance

Abstract: Caffeine is a popular ergogenic aid due to its primary physiological effects that occur through antagonism of adenosine receptors in the central nervous system. This leads to a cascade of physiological reactions which increases focus and volition, and reduces perception of effort and pain, contributing to improved exercise performance. Substantial variability in the physiological and performance response to acute caffeine consumption is apparent, and a growing number of studies are implicating a single-nucleotide polymorphism in the CYP1A2 gene, responsible for caffeine metabolism, as a key factor that influences the acute responses to caffeine ingestion. However, existing literature regarding the influence of this polymorphism on the ergogenic effects of caffeine is controversial. Fast caffeine metabolisers (AA homozygotes) appear most likely to benefit from caffeine supplementation, although over half of studies showed no differences in the responses to caffeine between CYP1A2 genotypes, while others even showed either a possible advantage or disadvantage for C-allele carriers. Contrasting data are limited by weak study designs and small samples sizes, which did not allow separation of C-allele carriers into their sub-groups (AC and CC), and insufficient mechanistic evidence to elucidate findings. Mixed results prevent practical recommendations based upon genotype while genetic testing for CYP1A2 is also currently unwarranted. More mechanistic and applied research is required to elucidate how the CYP1A2 polymorphism might alter caffeine's ergogenic effect and the magnitude thereof, and whether CYP1A2 genotyping prior to caffeine supplementation is necessary.

Individual cardiovascular responsiveness to work-matched exercise within the moderate- and severe-intensity domains

Abstract: We investigated the cardiovascular individual response to 6 weeks (3×/week) of work-matched within the severe-intensity domain (high-intensity interval training, HIIT) or moderate-intensity domain (moderate-intensity continuous training, MICT). In addition, we analyzed the cardiovascular factors at baseline underlying the response variability. 42 healthy sedentary participants were randomly assigned to HIIT or MICT. We applied the region of practical equivalence-method for identifying the levels of responders to the maximal oxygen uptake (VO2max) response. For investigating the influence of cardiovascular markers, we trained a Bayesian machine learning model on cardiovascular markers. Despite that HIIT and MICT induced significant increases in VO2max, HIIT had greater improvements than MICT (p < 0.001). Greater variability was observed in MICT, with approximately 50% classified as “non-responder” and “undecided”. 20 “responders”, one “undecided” and no “non-responders” were observed in HIIT. The variability in the ∆VO2max was associated with initial cardiorespiratory fitness, arterial stiffness, and left-ventricular (LV) mass and LV end-diastolic diameter in HIIT; whereas, microvascular responsiveness and right-ventricular (RV) excursion velocity showed a significant association in MICT. Our findings highlight the critical influence of exercise-intensity domains and biological variability on the individual VO2max response. The incidence of “non-responders” in MICT was one third of the group; whereas, no “non-responders” were observed in HIIT. The incidence of “responders” was 11 out of 21 participants in MICT, and 20 out of 21 participants in HIIT. The response in HIIT showed associations with baseline fitness, arterial stiffness, and LV-morphology; whereas, it was associated with RV systolic function in MICT.

Fasted plasma asprosin concentrations are associated with menstrual cycle phase, oral contraceptive use and training status in healthy women.

Abstract: Asprosin, an orexigenic hormone that stimulates hepatic glucose release, is elevated in insulin resistance and associated with obesity. Plasma asprosin concentrations may also be related to female sex hormone levels; higher levels are reported in women with polycystic ovary syndrome (PCOS) but this may be related to peripheral insulin resistance also associated with PCOS. Clarification of female-specific factors influence on the plasma asprosin response is crucial for studies investigating asprosin. Therefore, this study determined the association of menstrual phase, oral contraceptive (OC) use (as a pharmacological influence on sex hormone levels) and training status (as a physiological influence on sex hormone levels) on plasma asprosin levels in pre-menopausal women. Fasting plasma asprosin, 17β-estradiol (E2) and progesterone, were assessed in 32 healthy untrained and trained women with regular menstrual cycles (non-OC; n = 8 untrained, n = 6 trained) or using OC (n = 10 untrained, n = 8 trained) during early follicular, late follicular and mid-luteal menstrual phases (or the time-period equivalent for OC users). Asprosin was lower in OC (0.75 ± 0.38 ng mL−1) than non-OC users (1.00 ± 0.37 ng mL−1; p = 0.022). Across a cycle, asprosin was highest in the early follicular equivalent time-point in OC users (0.87 ± 0.37 ng mL−1) but highest in the mid-luteal phase in non-OC users (1.09 ± 0.40 ng mL−1). Asprosin concentrations varied more across a cycle in untrained than trained women, with higher concentrations in the early follicular phase compared to the late follicular and mid-luteal (training status-by-menstrual phase interaction p = 0.028). These findings highlight the importance of considering OC use, menstrual cycle phase and to a lesser extent training status when investigating circulating asprosin concentrations in females.

The effect of posture on maximal oxygen uptake in active healthy individuals.

Abstract: Semi-supine and supine cardiopulmonary exercise testing (CPET) with concurrent cardiac imaging has emerged as a valuable tool for evaluating patients with cardiovascular disease. Yet, it is unclear how posture effects CPET measures. We aimed to discern the effect of posture on maximal oxygen uptake (VO2max) and its determinants using three clinically relevant cycle ergometers. In random order, 10 healthy, active males (Age 27 ± 7 years; BMI 23 ± 2 kg m2) underwent a ramp CPET and subsequent constant workload verification test performed at 105% peak ramp power to quantify VO2max on upright, semi-supine and supine cycle ergometers. Doppler echocardiography was conducted at peak exercise to measure stroke volume (SV) which was multiplied by heart rate (HR) to calculate cardiac output (CO). Compared to upright (46.8 ± 11.2 ml/kg/min), VO2max was progressively reduced in semi-supine (43.8 ± 10.6 ml/kg/min) and supine (38.2 ± 9.3 ml/kg/min; upright vs. semi-supine vs. supine; all p ≤ 0.005). Similarly, peak power was highest in upright (325 ± 80 W), followed by semi-supine (298 ± 72 W) and supine (200 ± 51 W; upright vs. semi-supine vs. supine; all p < 0.01). Peak HR decreased progressively from upright to semi-supine to supine (186 ± 11 vs. 176 ± 13 vs. 169 ± 12 bpm; all p < 0.05). Peak SV and CO were lower in supine relative to semi-supine and upright (82 ± 22 vs. 92 ± 26 vs. 91 ± 24 ml and 14 ± 3 vs. 16 ± 4 vs. 17 ± 4 l/min; all p < 0.01), but not different between semi-supine and upright. VO2max is progressively reduced in reclined postures. Thus, posture should be considered when comparing VO2max results between different testing modalities.

Muscle architecture and morphology as determinants of explosive strength

Abstract: Neural drive and contractile properties are well-defined physiological determinants of explosive strength, the influence of muscle architecture and related morphology on explosive strength is poorly understood. The aim of this study was to examine the relationships between Quadriceps muscle architecture (pennation angle [ΘP] and fascicle length [FL]) and size (e.g., volume; QVOL), as well as patellar tendon moment arm (PTMA) with voluntary and evoked explosive knee extension torque in 53 recreationally active young men. Following familiarisation, explosive voluntary torque at 50 ms intervals from torque onset (T50, T100, T150), evoked octet at 50 ms (8 pulses at 300-Hz; evoked T50), as well as maximum voluntary torque, were assessed on two occasions with isometric dynamometry. B-mode ultrasound was used to assess ΘP and FL at ten sites throughout the quadriceps (2–3 sites) per constituent muscle. Muscle size (QVOL) and PTMA were quantified using 1.5 T MRI. There were no relationships with absolute early phase explosive voluntary torque (≤ 50 ms), but θP (weak), QVOL (moderate to strong) and PTMA (weak) were related to late phase explosive voluntary torque (≥ 100 ms). Regression analysis revealed only QVOL was an independent variable contributing to the variance in T100 (34%) and T150 (54%). Evoked T50 was also related to QVOL and θP. When explosive strength was expressed relative to MVT there were no relationships observed. It is likely that the weak associations of θP and PTMA with late phase explosive voluntary torque was via their association with MVT/QVOL rather than as a direct determinant.

The scaling of human basal and resting metabolic rates

Abstract: In tachymetabolic species, metabolic rate increases disproportionately with body mass, and that inter-specific relationship is typically modelled allometrically. However, intra-specific analyses are less common, particularly for healthy humans, so the possibility that human metabolism would also scale allometrically was investigated. Basal metabolic rate was determined (respirometry) for 68 males (18–40 years; 56.0–117.1 kg), recruited across five body-mass classes. Data were collected during supine, normothermic rest from well-rested, well-hydrated and post-absorptive participants. Linear and allometric regressions were applied, and three scaling methods were assessed. Data from an historical database were also analysed (2.7–108.9 kg, 4811 males; 2.0–96.4 kg, 2364 females). Both linear and allometric functions satisfied the statistical requirements, but not the biological pre-requisite of an origin intercept. Mass-independent basal metabolic data beyond the experimental mass range were not achieved using linear regression, which yielded biologically impossible predictions as body mass approached zero. Conversely, allometric regression provided a biologically valid, powerful and statistically significant model: metabolic rate = 0.739 * body mass0.547 (P < 0.05). Allometric analysis of the historical male data yielded an equivalent, and similarly powerful model: metabolic rate = 0.873 * body mass0.497 (P < 0.05). It was established that basal and resting metabolic rates scale allometrically with body mass in humans from 10–117 kg, with an exponent of 0.50–0.55. It was also demonstrated that ratiometric scaling yielded invalid metabolic predictions, even within the relatively narrow experimental mass range. Those outcomes have significant physiological implications, with applications to exercising states, modelling, nutrition and metabolism-dependent pharmacological prescriptions.

Eccentric exercise per se does not affect muscle damage biomarkers: early and late phase adaptations.

Abstract: Acute high-intensity unaccustomed eccentric exercise performed by naive subjects is accompanied by disturbances in muscle damage biomarkers. The aim of the study was to investigate whether a causal relationship indeed exists between eccentric exercise and muscle damage. Twenty-four men randomly assigned into a concentric only or an eccentric-only training group and performed 10 weeks of isokinetic resistance exercise (one session/week of 75 maximal knee extensors actions). Physiological markers of muscle function and damage (i.e., range of motion, delayed onset muscle soreness, isometric, concentric and eccentric peak torque) were assessed prior to and 1–3 and 5 days post each session. Biochemical markers of muscle damage (creatine kinase) and inflammation (C-reactive protein) were measured prior and 2 days post each session. After the first bout, eccentric exercise induced greater muscle damage compared to concentric exercise; however, during the nine following sessions, this effect progressively diminished, while after the 10th week of training, no alterations in muscle damage biomarkers were observed after either exercise protocol. Additionally, strength gains at the end of the training period were comparable between the two groups and were mode-specific. (1) eccentric exercise per se does not affect muscle damage biomarkers; (2) muscle damage occurs as a result of muscle unaccustomedness to this action type; (3) exercise-induced muscle damage is not a prerequisite for increased muscle strength. Collectively, we believe that muscle unaccustomedness to high-intensity eccentric exercise, and not eccentric exercise per se, is the trigger for muscle damage as indicated by muscle damage biomarkers.

Sex differences in the physiological adaptations to heat acclimation: a state-of-the-art review

Abstract: Over the last few decades, females have significantly increased their participation in athletic competitions and occupations (e.g. military, firefighters) in hot and thermally challenging environments. Heat acclimation, which involves repeated passive or active heat exposures that lead to physiological adaptations, is a tool commonly used to optimize performance in the heat. However, the scientific community's understanding of adaptations to heat acclimation are largely based on male data, complicating the generalizability to female populations. Though limited, current evidence suggests that females may require a greater number of heat acclimation sessions or greater thermal stress to achieve the same magnitude of physiological adaptations as males. The underlying mechanisms explaining the temporal sex differences in the physiological adaptations to heat acclimation are currently unclear. Therefore, the aims of this state-of-the-art review are to: (i) present a brief yet comprehensive synthesis of the current female and sex difference literature, (ii) highlight sex-dependent (e.g. anthropometric, menstrual cycle) and sex-independent factors (e.g. environmental conditions, fitness) influencing the physiological and performance adaptations to heat acclimation, and (iii) address key avenues for future research.

Corticospinal and spinal adaptations to motor skill and resistance training: Potential mechanisms and implications for motor rehabilitation and athletic development

Abstract: Optimal strategies for enhancing strength and improving motor skills are vital in athletic performance and clinical rehabilitation. Initial increases in strength and the acquisition of new motor skills have long been attributed to neurological adaptations. However, early increases in strength may be predominantly due to improvements in inter-muscular coordination rather than the force-generating capacity of the muscle. Despite the plethora of research investigating neurological adaptations from motor skill or resistance training in isolation, little effort has been made in consolidating this research to compare motor skill and resistance training adaptations. The findings of this review demonstrated that motor skill and resistance training adaptations show similar short-term mechanisms of adaptations, particularly at a cortical level. Increases in corticospinal excitability and a release in short-interval cortical inhibition occur as a result of the commencement of both resistance and motor skill training. Spinal changes show evidence of task-specific adaptations from the acquired motor skill, with an increase or decrease in spinal reflex excitability, dependant on the motor task. An increase in synaptic efficacy of the reticulospinal projections is likely to be a prominent mechanism for driving strength adaptations at the subcortical level, though more research is needed. Transcranial electric stimulation has been shown to increase corticospinal excitability and augment motor skill adaptations, but limited evidence exists for further enhancing strength adaptations from resistance training. Despite the logistical challenges, future work should compare the longitudinal adaptations between motor skill and resistance training to further optimise exercise programming.

Changes in gastrointestinal cell integrity after marathon running and exercise-associated collapse

Abstract: Endurance exercise and hyperthermia are associated with compromised intestinal permeability and endotoxaemia. The presence of intestinal fatty acid-binding protein (I-FABP) in the systemic circulation suggests intestinal wall damage, but this marker has not previously been used to investigate intestinal integrity after marathon running. Twenty-four runners were recruited as controls prior to completing a standard marathon and had sequential I-FABP measurements before and on completion of the marathon, then at four and 24 h later. Eight runners incapacitated with exercise-associated collapse (EAC) with hyperthermia had I-FABP measured at the time of collapse and 1 hour later. I-FABP was increased immediately on completing the marathon (T0; 2593 ± 1373 ng·l−1) compared with baseline (1129 ± 493 ng·l−1; p < 0.01) in the controls, but there was no significant difference between baseline and the levels at four hours (1419 ± 1124 ng·l−1; p = 0.7), or at 24 h (1086 ± 302 ng·l−1; p = 0.5). At T0, EAC cases had a significantly higher I-FABP concentration (15,389 ± 8547 ng.l−1) compared with controls at T0 (p < 0.01), and remained higher at 1 hour after collapse (13,951 ± 10,476 ng.l−1) than the pre-race control baseline (p < 0.05). I-FABP is a recently described biomarker whose presence in the circulation is associated with intestinal wall damage. I-FABP levels increase after marathon running and increase further if the endurance exercise is associated with EAC and hyperthermia. After EAC, I-FABP remains high in the circulation for an extended period, suggesting ongoing intestinal wall stress.