Effects of CurraNZ, a New Zealand Blackcurrant Extract during 1 Hour of Treadmill Running in Female and Male Marathon des Sables Athletes in Hot Conditions: Two Case Studies

Four weeks before competition in the 2023 Marathon des Sables, a 6-stage, ~250 km running event in the Sahara Desert, we examined the effects of a 7-day intake of New Zealand blackcurrant extract (210 mg anthocyanins per day) on 1 h treadmill running-induced physiological and metabolic responses in the heat (~34 °C, relative humidity: ~30%) in non-acclimatized amateur female and male athletes (age: 23, 38 yrs, BMI: 24.2, 28.4 kg·m-2, body fat%: 29.2, 18.8%, V˙O2max: 50.1, 52.1 mL·kg-1·min-1). During the 1 h run at 50%V˙O2max (speed female: 7.3, male: 7.5 km·h-1), indirect calorimetry was used, and heart rate was recorded at 15 min intervals with core temperature monitoring (0.05 Hz). The 1 h runs took place 3 h after a light breakfast and 2 h after intake of the final dose of New Zealand blackcurrant extract with water allowed ad libitum during the run. The New Zealand blackcurrant extract had no effects on the female athlete. The respiratory exchange ratio (RER) of the female athlete in the non-supplement control condition was 0.77 ± 0.01, indicating an existing ~77% contribution of fat oxidation to the energy requirements. In the male athlete, during 1 h of running, fat oxidation was higher by 21% (p < 0.01), carbohydrate oxidation was 31% lower (p = 0.05), RER was 0.03 units lower (p = 0.04), and core temperature was 0.4 °C lower (p < 0.01) with no differences for heart rate, minute ventilation, oxygen uptake, and carbon dioxide production for the New Zealand blackcurrant condition compared to the non-supplement control condition. Seven-day intake of New Zealand blackcurrant extract (210 mg anthocyanins per day) provided beneficial physiological and metabolic responses during exertional heat stress by 1 h of indoor (~34 °C) treadmill running in a male Marathon des Sables athlete 4 weeks before competition. Future work is required to address whether New Zealand blackcurrant provides a nutritional ergogenic effect for Marathon des Sables athletes during long-duration running in the heat combined with personalized nutrition.

Peak fat oxidation, peak oxygen uptake, and running performance increase during pre-season in sub-elite male football players

PURPOSE

In Football, the high-intensity running bouts during matches are considered decisive. Interestingly, recent studies showed that peak fat oxidation rates (PFO) are higher in football players than other athletes. This study aimed to investigate whether PFO increases following a pre-season. Secondarily, and due to COVID-19, we investigated whether PFO is related to the physical performance in a subgroup of semi-professional male football players.

METHODS

Before and after 8 weeks of pre-season training, 42 sub-elite male football players (18 semi-professionals and 24 non-professionals) had a dual-energy x-ray absorptiometry scan and performed a graded exercise test on a treadmill for the determination of PFO, the exercise intensity eliciting PFO (Fatmax) and peak oxygen uptake (V̇O2peak). Additionally, the semi-professional players performed a Yo-Yo Intermittent Recovery Test level 2 (YYIR2) before and after pre-season training to determine football-specific running performance.

RESULTS

PFO increased by 11 ± 10% (mean ± 95% CI), p = 0.031, and V̇O2peak increased by 5 ± 1%, p < 0.001, whereas Fatmax was unchanged (+12 ± 9%, p = 0.057), following pre-season training. PFO increments were not associated with increments in V̇O2peak (Pearson's r2 = 0.00, p = 0.948) or fat-free mass (FFM) (r2 = 0.00, p = 0.969). Concomitantly, YYIR2 performance increased in the semi-professional players by 39 ± 17%, p < 0.001, which was associated with changes in V̇O2peak (r2 = 0.35, p = 0.034) but not PFO (r2 = 0.13, p = 0.244).

CONCLUSIONS

PFO, V̇O2peak, and FFM increased following pre-season training in sub-elite football players. However, in a subgroup of semi-professional players, increments in PFO were not associated with improvements in YYIR2 performance nor with increments in V̇O2peak and FFM.

Comparison of Concurrent and Asynchronous Running Kinematics and Kinetics From Marker-Based and Markerless Motion Capture Under Varying Clothing Conditions

As markerless motion capture is increasingly used to measure 3-dimensional human pose, it is important to understand how markerless results can be interpreted alongside historical marker-based data and how they are impacted by clothing. We compared concurrent running kinematics and kinetics between marker-based and markerless motion capture, and between 2 markerless clothing conditions. Thirty adults ran on an instrumented treadmill wearing motion capture clothing while concurrent marker-based and markerless data were recorded, and ran a second time wearing athletic clothing (shorts and t-shirt) while markerless data were recorded. Differences calculated between the concurrent signals from both systems, and also between each participant's mean signals from both asynchronous clothing conditions were summarized across all participants using root mean square differences. Most kinematic and kinetic signals were visually consistent between systems and markerless clothing conditions. Between systems, joint center positions differed by 3 cm or less, sagittal plane joint angles differed by 5° or less, and frontal and transverse plane angles differed by 5° to 10°. Joint moments differed by 0.3 N·m/kg or less between systems. Differences were sensitive to segment coordinate system definitions, highlighting the effects of these definitions when comparing against historical data or other motion capture modalities.

Reliability of Xsens inertial measurement unit in measuring trunk accelerations: a sex-based differences study during incremental treadmill running

Introduction

Inertial measurement units (IMUs) are utilized to measure trunk acceleration variables related to both running performances and rehabilitation purposes. This study examined both the reliability and sex-based differences of these variables during an incremental treadmill running test.

Methods

Eighteen endurance runners performed a test-retest on different days, and 30 runners (15 females) were recruited to analyze sex-based differences. Mediolateral (ML) and vertical (VT) trunk displacement and root mean square (RMS) accelerations were analyzed at 9, 15, and 21 km·h-1.

Results

No significant differences were found between test-retests [effect size (ES)<0.50)]. Higher intraclass correlation coefficients (ICCs) were found in the trunk displacement (0.85-0.96) compared to the RMS-based variables (0.71-0.94). Male runners showed greater VT displacement (ES = 0.90-1.0), while female runners displayed greater ML displacement, RMS ML and anteroposterior (AP), and resultant euclidean scalar (RES) (ES = 0.83-1.9).

Discussion

The IMU was found reliable for the analysis of the studied trunk acceleration-based variables. This is the first study that reports different results concerning acceleration (RMS) and trunk displacement variables for a same axis in the analysis of sex-based differences.

Effects of Different Wearable Resistance Placements on Running Stability

Stability during running has been recognized as a crucial factor contributing to running performance. This study aimed to investigate the effects of wearable equipment containing external loads on different body parts on running stability. Fifteen recreational male runners (20.27 ± 1.23 years, age range 19-22 years) participated in five treadmill running conditions, including running without loads and running with loads equivalent to 10% of individual body weight placed on four different body positions: forearms, lower legs, trunk, and a combination of all three (forearms, lower legs, and trunk). A tri-axial accelerometer-based smartphone sensor was attached to the participants' lumbar spine (L5) to record body accelerations. The largest Lyapunov exponent (LyE) was applied to individual acceleration data as a measure of local dynamic stability, where higher LyE values suggest lower stability. The effects of load distribution appear in the mediolateral (ML) direction. Specifically, running with loads on the lower legs resulted in a lower LyE_ML value compared to running without loads (p = 0.001) and running with loads on the forearms (p < 0.001), trunk (p = 0.001), and combined segments (p = 0.005). These findings suggest that running with loads on the lower legs enhances side-to-side local dynamic stability, providing valuable insights for training.

Establishment of a Neurodegenerative Charcot Mouse Model

BACKGROUND

This study aimed to mimic the changes from Charcot neuropathic arthropathy in humans by examining the effects of exposing diet-induced obese (DIO) mice to neurotrauma through a regimented running protocol.

METHODS

Forty-eight male wild-type C57BL/6J mice were obtained at age 6 weeks and separated into 2 groups for diet assignment. After a 1-week acclimation period, half of the mice consumed a high-fat diet (60% fat by kcal) ad libitum to facilitate neuropathic diet-induced obesity whereas the other half were control mice and consumed an age-matched standard low-fat control diet (10% fat by kcal). At age 12 weeks, half of the animals from each group were subjected to a high-intensity inclined treadmill running protocol, which has been previously demonstrated to induce neurotrauma. Sensory testing and radiographic analyses were periodically performed. Histopathologic analyses were performed post killing.

RESULTS

DIO mice had significantly higher bodyweights, higher body fat percentages, and lower bone mineral density than wildtype control mice that were fed a normal diet throughout the experiment (P < .001 for each). DIO mice displayed significantly reduced sensory function in week 1 (P = .005) and this worsened over time, requiring 20.6% more force for paw withdrawal by week 10 (P < .001). DIO mice that ran demonstrated greater midfoot subluxation and tarsal instability over all time points compared with normal-diet mice that ran (P < .001). Histopathologic analyses revealed that DIO mice that ran demonstrated significant changes compared with controls that ran (P < .001 for each parameter).

CONCLUSION

Changes akin to the earliest changes observed in or before joint destruction identified in diabetic Charcot neuropathic arthropathy in humans were observed.

CLINICAL RELEVANCE

There is currently no standard of treatment for patients with Charcot neuropathic arthropathy. This study establishes a protocol for an animal model that can be used to study and compare interventions to treat this disease.

Hypoxia with or without Treadmill Exercises Affects Slow-Twitch Muscle Atrophy and Joint Destruction in a Rat Model of Rheumatoid Arthritis

The effects of treadmill running under hypoxic conditions on joints and muscles of collagen-induced arthritis (CIA) rats were investigated. CIA rats were divided into normoxia no-exercise, hypoxia no-exercise (Hypo-no), and hypoxia exercise (Hypo-ex) groups. Changes were examined on days 2 and 44 of hypoxia with or without treadmill exercises. In the early stage of hypoxia, the expression of hypoxia-inducible factor (HIF)-1α increased in the Hypo-no and Hypo-ex groups. The expression of the egl-9 family hypoxia-inducible factor 1 (EGLN1) and vascular endothelial growth factor (VEGF) in the Hypo-ex group also increased. Under sustained hypoxia, the Hypo-no and Hypo-ex groups did not show increased expression of HIF-1α or VEGF, but p70S6K levels were elevated. Histologically, joint destruction was alleviated in the Hypo-no group, the loss of muscle weight in slow-twitch muscles was prevented, and muscle fibrosis was suppressed. In the Hypo-ex group, the preventive effect of a reduction in the slow-twitch muscle cross-sectional area was enhanced. Thus, chronic hypoxia in an animal model of rheumatoid arthritis controlled arthritis and joint destruction and prevented slow-twitch muscle atrophy and fibrosis. The combination of hypoxia with treadmill running further enhanced the preventive effects on slow-twitch muscle atrophy.

Effects of exercise intensity on the reactive astrocyte polarization in the medial prefrontal cortex

PURPOSE

Physical exercise contributes to neuroplasticity by promoting cognitive functions, such as learning and memory. The astrocytic phenotype is closely associated with synaptic plasticity. This study aimed to determine whether astrocyte polarization and synaptic alterations in the medial prefrontal cortex (mPFC) are affected differently by high- and moderate-intensity exercise.

METHODS

Mice were subjected to moderate-(MIE) and high-intensity treadmill running (HIE). Memory capacity was assessed using the novel object recognition and modified Y-maze tests. For immunohistochemistry, c-Fos-positive cells were counted in the mPFC. Using western blot analysis, astrocyte phenotype markers were quantified in whole-cell lysates, and synaptic molecules were determined in the synaptosomal fraction.

RESULTS

Exercise lengthened the approach time to novel objects regardless of intensity in the NOR test, whereas MIE only improved spatial memory. Exercise induced c-Fos expression in the anterior cingulate cortex (ACC) and c-Fos-positive cells were higher in MIE than in HIE in the ACC area. In the prelimbic/infralimbic cortex region, the number of c-Fos-positive cells were enhanced in MIE and decreased in HIE mice. The A1 astrocyte marker (C3) was increased in HIE mice, while the A2 astrocyte markers were enhanced in exercised mice, regardless of the intensity. In the synaptosomal fraction, synaptic proteins were elevated by exercise regardless of intensity.

CONCLUSION

These results suggest that exercise intensity affects neuronal plasticity by modulating the reactive state of astrocytes in the mPFC.

Reliability of Soft Tissue Vibration Measurement and Number of Steps Demanded during Treadmill Running

The present study aims to determine the test-retest reliability of the input signal (INPUT) of foot impact and soft tissue vibration (STV) of the lower limb muscles during treadmill running. Twenty-six recreational runners participated in three running trials at constant velocity (10 km/h) within two days. The INPUT and STV of gastrocnemius medialis (GAS) and vastus lateralis (VL) were extracted from 100 steps measured by three triaxial accelerometers. The Intraclass Correlation Coefficient (ICC) was calculated to determine the Intra-trial and Inter-day reliability of the different variables. Intra-trial reliability results indicated that most of the INPUT and GAS STV parameters, except for damping coefficient and setting time, have good to excellent reliability (0.75 < ICC < 0.9) from the beginning of the run (10 steps) to the end. In contrast, only 4 VL STV parameters showed good reliability. Furthermore, inter-trial reliability measured on day one showed that the number of reliable parameters reduced, especially for VL STV, and more steps were required (20 < steps < 80) to achieve good reliability. Inter-day reliability results showed that only one VL STV parameter reached good reliability. Therefore, the present results show that the measurement of the foot impact and the calf muscle vibrations present a good to excellent reliability measured on a single trial and two trials carried out on the same day. The reliability of these parameters remains good when comparing two days of experimentation. We recommend measuring impact and STV parameters during treadmill running in the same session.

Effects of treadmill exercise and chronic stress on anxiety-like behavior, neuronal activity, and oxidative stress in basolateral amygdala in morphine-treated rats

The basolateral amygdala (BLA), which is sensitive to stress, is necessary for reward-seeking behavior and addiction. Regular exercise can produce various positive effects by affecting the BLA. Therefore, we aimed to investigate the effects of chronic stress and treadmill running (TR) on anxiety-like behavior, neuronal activity, lipid peroxidation (measured by malondialdehyde (MDA) levels, a marker for oxidative stress), and total thiol in BLA, in morphine-treated rats. Male Wistar rats were restricted in restraint stress and/or ran on the treadmill and treated with morphine (5 mg/kg) for 21 days. Anxiety-like behavior was evaluated using an elevated plus maze (EPM) and open field tests (OFTs), on day 22. On day 23, neuronal activity in BLA was assessed via single-unit recording. Finally, MDA and total thiol were assessed in BLA. Our results showed that chronic administration of morphine (5 mg/kg) did not affect anxiety-like behavior. However, the morphine-treated rats, subjected to chronic stress and exercise, showed fewer anxiety-like behaviors. Morphine increased BLA's MDA levels but it was prevented by TR. Glutamatergic and GABAergic basal neuronal activities were low in morphine-treated rats but after acute morphine application, there was a significant decrease in GABAergic neuronal activities in the morphine-exercise-stress (Mor-Exe-St) group. The results of this study showed that in morphine-treated rats, stress and exercise or their combination could have either co-directional or opposite effects to the chronic effects of morphine. These results indicate the existence of common pathways similar to endogenous opioids.

Effects of compression running pants and treadmill running stages on knee proprioception and fatigue-related physiological responses in half-marathon runners

Background: Knee injury is common in half-marathon runners, however, the effect of compression running pants on fatigue and knee proprioception remains unclear. Objectives: The study aims to investigate whether wearing compression running pants (CRP) and treadmill running stages affect knee proprioception and fatigue-related physiological responses during half-marathon running. Methods: Eighteen half-marathon runners completed two self-paced 21 km treadmill running trials, once wearing CRP and once wearing loose running shorts (LRS). For each 21 km run, RPE, heart rate, blood lactic acid, and knee flexion proprioception were assessed before starting, and after each 7 km stage. Results: Data analysis revealed no difference between CRP and LRS conditions in heart rate, RPE, or blood lactic acid. Repeated measures ANOVA showed a significant garment condition main effect whereby wearing CRP was associated with higher knee proprioceptive acuity (p = 0.006). Polynomial trend analysis showed a significant linear downwards trend in proprioceptive acuity across the four measurement occasions (p = 0.048). Stage analysis showed that wearing CRP was associated with better knee proprioception at running distances of 14 km (p = 0.007, 95%CI = -0.054, -0.010) and 21 km (p = 0.016, 95%CI = -0.051, -0.006). Conclusion: Compression running pants provide an overall positive effect on knee proprioception, particularly after 14 km and 21km, which may reduce the probability of knee injury. CRP had no significant effect on physiological measures in half-marathon running.

Antioxidant Molecular Brain Changes Parallel Adaptive Cardiovascular Response to Forced Running in Mice

Physically active lifestyle has huge implications for the health and well-being of people of all ages. However, excessive training can lead to severe cardiovascular events such as heart fibrosis and arrhythmia. In addition, strenuous exercise may impair brain plasticity. Here we investigate the presence of any deleterious effects induced by chronic high-intensity exercise, although not reaching exhaustion. We analyzed cardiovascular, cognitive, and cerebral molecular changes in young adult male mice submitted to treadmill running for eight weeks at moderate or high-intensity regimens compared to sedentary mice. Exercised mice showed decreased weight gain, which was significant for the high-intensity group. Exercised mice showed cardiac hypertrophy but with no signs of hemodynamic overload. No morphological changes in the descending aorta were observed, either. High-intensity training induced a decrease in heart rate and an increase in motor skills. However, it did not impair recognition or spatial memory, and, accordingly, the expression of hippocampal and cerebral cortical neuroplasticity markers was maintained. Interestingly, proteasome enzymatic activity increased in the cerebral cortex of all trained mice, and catalase expression was significantly increased in the high-intensity group; both first-line mechanisms contribute to maintaining redox homeostasis. Therefore, physical exercise at an intensity that induces adaptive cardiovascular changes parallels increases in antioxidant defenses to prevent brain damage.

Sex Difference in Running Stability Analyzed Based on a Whole-Body Movement: A Pilot Study

A sex-specific manner in running tasks is considered a potential internal injury risk factor in runners. The current study aimed to investigate the sex differences in running stability in recreational runners during self-preferred speed treadmill running by focusing on a whole-body movement. To this end, principal component analysis (PCA) was applied to kinematic marker data of 22 runners (25.7 ± 3.3 yrs.; 12 females) for decomposing the whole-body movements of all participants into a set of principal movements (PMs), representing different movement synergies forming together to achieve the task goal. Then, the sex effects were tested on three types of PCA-based variables computed for individual PMs: the largest Lyapunov exponent (LyE) as a measure of running variability; the relative standard deviation (rSTD) as a measure of movement structures; and the root mean square (RMS) as a measure of the magnitude of neuromuscular control. The results show that the sex effects are observed in the specific PMs. Specifically, female runners have lower stability (greater LyE) in the mid-stance-phase movements (PM₄₋₅) and greater contribution and control (greater rSTD and RMS) in the swing-phase movement (PM₁) than male runners. Knowledge of an inherent sex difference in running stability may benefit sports-related injury prevention and rehabilitation.

Impact of Treadmill Interval Running on the Appearance of Zinc Finger Protein FHL2 in Bone Marrow Cells in a Rat Model: A Pilot Study

Although the benefits of physical exercise to preserve bone quality are now widely recognized, the intimate mechanisms leading to the underlying cell responses still require further investigations. Interval training running, for instance, appears as a generator of impacts on the skeleton, and particularly on the progenitor cells located in the bone marrow. Therefore, if this kind of stimulus initiates bone cell proliferation and differentiation, the activation of a devoted signaling pathway by mechano-transduction seems likely. This study aimed at investigating the effects of an interval running program on the appearance of the zinc finger protein FHL2 in bone cells and their anatomical location. Twelve 5-week-old male Wistar rats were randomly allocated to one of the following groups (n = 6 per group): sedentary control (SED) or high-intensity interval running (EX, 8 consecutive weeks). FHL2 identification in bone cells was performed by immuno-histochemistry on serial sections of radii. We hypothesized that impacts generated by running could activate, in vivo, a specific signaling pathway, through an integrin-mediated mechano-transductive process, leading to the synthesis of FHL2 in bone marrow cells. Our data demonstrated the systematic appearance of FHL2 (% labeled cells: 7.5%, p < 0.001) in bone marrow obtained from EX rats, whereas no FHL2 was revealed in SED rats. These results suggest that the mechanical impacts generated during high-intensity interval running activate a signaling pathway involving nuclear FHL2, such as that also observed with dexamethasone administration. Consequently, interval running could be proposed as a non-pharmacological strategy to contribute to bone marrow cell osteogenic differentiation.

Systematic Review and Meta-Analysis of Endurance Exercise Training Protocols for Mice

Inbred and genetically modified mice are frequently used to investigate the molecular mechanisms responsible for the beneficial adaptations to exercise training. However, published paradigms for exercise training in mice are variable, making comparisons across studies for training efficacy difficult. The purpose of this systematic review and meta-analysis was to characterize the diversity across published treadmill-based endurance exercise training protocols for mice and to identify training protocol parameters that moderate the adaptations to endurance exercise training in mice. Published studies were retrieved from PubMed and EMBASE and reviewed for the following inclusion criteria: inbred mice; inclusion of a sedentary group; and exercise training using a motorized treadmill. Fifty-eight articles met those inclusion criteria and also included a "classical" marker of training efficacy. Outcome measures included changes in exercise performance, V ˙ O_2max, skeletal muscle oxidative enzyme activity, blood lactate levels, or exercise-induced cardiac hypertrophy. The majority of studies were conducted using male mice. Approximately 48% of studies included all information regarding exercise training protocol parameters. Meta-analysis was performed using 105 distinct training groups (i.e., EX-SED pairs). Exercise training had a significant effect on training outcomes, but with high heterogeneity (Hedges' g=1.70, 95% CI=1.47-1.94, Tau²=1.14, I² =80.4%, prediction interval=-0.43-3.84). Heterogeneity was partially explained by subgroup differences in treadmill incline, training duration, exercise performance test type, and outcome variable. Subsequent analyses were performed on subsets of studies based on training outcome, exercise performance, or biochemical markers. Exercise training significantly improved performance outcomes (Hedges' g=1.85, 95% CI=1.55-2.15). Subgroup differences were observed for treadmill incline, training duration, and exercise performance test protocol on improvements in performance. Biochemical markers also changed significantly with training (Hedges' g=1.62, 95% CI=1.14-2.11). Subgroup differences were observed for strain, sex, exercise session time, and training duration. These results demonstrate there is a high degree of heterogeneity across exercise training studies in mice. Training duration had the most significant impact on training outcome. However, the magnitude of the effect of exercise training varies based on the marker used to assess training efficacy.

Mechanical Overloading Induced-Activation of mTOR Signaling in Tendon Stem/Progenitor Cells Contributes to Tendinopathy Development

Despite the importance of mechanical loading in tendon homeostasis and pathophysiology, the molecular responses involved in the mechanotransduction in tendon cells remain unclear. In this study, we found that in vitro mechanical loading activated the mammalian target of rapamycin (mTOR) in rat patellar tendon stem/progenitor cells (TSCs) in a stretching magnitude-dependent manner. Application of rapamycin, a specific inhibitor of mTOR, attenuated the phosphorylation of S6 and 4E-BP1 and as such, largely inhibited the mechanical activation of mTOR. Moreover, rapamycin significantly decreased the proliferation and non-tenocyte differentiation of PTSCs as indicated by the reduced expression levels of LPL, PPARγ, SOX-9, collagen II, Runx-2, and osteocalcin genes. In the animal studies, mice subjected to intensive treadmill running (ITR) developed tendon degeneration, as evidenced by the formation of round-shaped cells, accumulation of proteoglycans, and expression of SOX-9 and collagen II proteins. However, daily injections of rapamycin in ITR mice reduced all these tendon degenerative changes. Collectively, these findings suggest that mechanical loading activates the mTOR signaling in TSCs, and rapamycin may be used to prevent tendinopathy development by blocking non-tenocyte differentiation due to mechanical over-activation of mTOR in TSCs.

A New Fitness Test of Estimating VO2max in Well-Trained Rowing Athletes

Background

This study was designed to investigate the validity of maximal oxygen consumption (VO_2max) estimation through the Firstbeat fitness test (FFT) method when using submaximal rowing and running programs for well-trained athletes.

Methods

Well-trained flatwater rowers (n = 45, 19.8 ± 3.0 years, 184 ± 8.7 cm, 76 ± 12.9 kg, and 58.7 ± 6.0 mL⋅kg^–1⋅min^–1) and paddlers (n = 45, 19.0 ± 2.5 years, 180 ± 7.7 cm, 74 ± 9.4 kg, and 59.9 ± 4.8 mL⋅kg^–1⋅min^–1) completed the FFT and maximal graded exercise test (GXT) programs of rowing and running, respectively. The estimated VO_2max was calculated using the FFT system, and the measured VO_2max was obtained from the GXT programs. Differences between the estimated and measured VO_2max values were analyzed to assess the accuracy and agreement of the predictions. Equations from the previous study were also used to predict the VO_2max in the submaximal programs to compare the accuracy of prediction with the FFT method.

Results

The FFT method was in good agreement with the measured VO_2max in both groups based on the intraclass correlation coefficients (>0.8). Additionally, the FFT method had considerable accuracy in VO_2max estimation as the mean absolute percentage error (≤5.0%) and mean absolute error (<3.0 mL⋅kg^–1⋅min^–1) were fairly low. Furthermore, the FFT method seemed more accurate in the estimation of VO_2max than previously reported equations, especially in the rowing test program.

Conclusion

This study revealed that the FFT method provides a considerably accurate estimation of VO_2max in well-trained athletes.

Treadmill Running Changes Endothelial Lipase Expression: Insights from Gene and Protein Analysis in Various Striated Muscle Tissues and Serum

Endothelial lipase (EL) is an enzyme capable of HDL phospholipids hydrolysis. Its action leads to a reduction in the serum high-density lipoprotein concentration, and thus, it exerts a pro-atherogenic effect. This study examines the impact of a single bout exercise on the gene and protein expression of the EL in skeletal muscles composed of different fiber types (the soleus—mainly type I, the red gastrocnemius—mostly IIA, and the white gastrocnemius—predominantly IIX fibers), as well as the diaphragm, and the heart. Wistar rats were subjected to a treadmill run: (1) t = 30 [min], V = 18 [m/min]; (2) t = 30 [min], V = 28 [m/min]; (3) t = 120 [min], V = 18 [m/min] (designated: M30, F30, and M120, respectively). We established EL expression in the total muscle homogenates in sedentary animals. Resting values could be ordered with the decreasing EL protein expression as follows: endothelium of left ventricle > diaphragm > red gastrocnemius > right ventricle > soleus > white gastrocnemius. Furthermore, we observed that even a single bout of exercise was capable of inducing changes in the mRNA and protein level of EL, with a clearer pattern observed for the former. After 30 min of running at either exercise intensity, the expression of EL transcript in all the cardiovascular components of muscles tested, except the soleus, was reduced in comparison to the respective sedentary control. The protein content of EL varied with the intensity and/or duration of the run in the studied whole tissue homogenates. The observed differences between EL expression in vascular beds of muscles may indicate the muscle-specific role of the lipase.

Quantitative and Qualitative Running Gait Analysis through an Innovative Video-Based Approach

Quantitative and qualitative running gait analysis allows the early identification and the longitudinal monitoring of gait abnormalities linked to running-related injuries. A promising calibration- and marker-less video sensor-based technology (i.e., Graal), recently validated for walking gait, may also offer a time- and cost-efficient alternative to the gold-standard methods for running. This study aim was to ascertain the validity of an improved version of Graal for quantitative and qualitative analysis of running. In 33 healthy recreational runners (mean age 41 years), treadmill running at self-selected submaximal speed was simultaneously evaluated by a validated photosensor system (i.e., Optogait—the reference methodology) and by the video analysis of a posterior 30-fps video of the runner through the optimized version of Graal. Graal is video analysis software that provides a spectral analysis of the brightness over time for each pixel of the video, in order to identify its frequency contents. The two main frequencies of variation of the pixel’s brightness (i.e., F1 and F2) correspond to the two most important frequencies of gait (i.e., stride frequency and cadence). The Optogait system recorded step length, cadence, and its variability (vCAD, a traditional index of gait quality). Graal provided a direct measurement of F2 (reflecting cadence), an indirect measure of step length, and two indexes of global gait quality (harmony and synchrony index). The correspondence between quantitative indexes (Cadence vs. F2 and step length vs. Graal step length) was tested via paired t-test, correlations, and Bland–Altman plots. The relationship between qualitative indexes (vCAD vs. Harmony and Synchrony Index) was investigated by correlation analysis. Cadence and step length were, respectively, not significantly different from and highly correlated with F2 (1.41 Hz ± 0.09 Hz vs. 1.42 Hz ± 0.08 Hz, p = 0.25, r² = 0.81) and Graal step length (104.70 cm ± 013.27 cm vs. 107.56 cm ± 13.67 cm, p = 0.55, r² = 0.98). Bland–Altman tests confirmed a non-significant bias and small imprecision between methods for both parameters. The vCAD was 1.84% ± 0.66%, and it was significantly correlated with neither the Harmony nor the Synchrony Index (0.21 ± 0.03, p = 0.92, r² = 0.00038; 0.21 ± 0.96, p = 0.87, r² = 0.00122). These findings confirm the validity of the optimized version of Graal for the measurement of quantitative indexes of gait. Hence, Graal constitutes an extremely time- and cost-efficient tool suitable for quantitative analysis of running. However, its validity for qualitative running gait analysis remains inconclusive and will require further evaluation in a wider range of absolute and relative running intensities in different individuals.

Beneficial Role of Exercise in the Modulation of mdx Muscle Plastic Remodeling and Oxidative Stress

Duchenne muscular dystrophy (DMD) is an X-linked recessive progressive lethal disorder caused by the lack of dystrophin, which determines myofibers mechanical instability, oxidative stress, inflammation, and susceptibility to contraction-induced injuries. Unfortunately, at present, there is no efficient therapy for DMD. Beyond several promising gene- and stem cells-based strategies under investigation, physical activity may represent a valid noninvasive therapeutic approach to slow down the progression of the pathology. However, ethical issues, the limited number of studies in humans and the lack of consistency of the investigated training interventions generate loss of consensus regarding their efficacy, leaving exercise prescription still questionable. By an accurate analysis of data about the effects of different protocol of exercise on muscles of mdx mice, the most widely-used pre-clinical model for DMD research, we found that low intensity exercise, especially in the form of low speed treadmill running, likely represents the most suitable exercise modality associated to beneficial effects on mdx muscle. This protocol of training reduces muscle oxidative stress, inflammation, and fibrosis process, and enhances muscle functionality, muscle regeneration, and hypertrophy. These conclusions can guide the design of appropriate studies on human, thereby providing new insights to translational therapeutic application of exercise to DMD patients.

Beneficial intergenerational effects of exercise on brain and cognition: a multilevel meta-analysis of mean and variance

Physical exercise not only helps to improve physical health but can also enhance brain development and cognition. Recent reports on parental (both maternal and paternal) effects raise the possibility that parental exercise may provide benefits to offspring through intergenerational inheritance. However, the general magnitude and consistency of parental exercise effects on offspring is still controversial. Additionally, empirical research has long overlooked an important aspect of exercise: its effects on variability in neurodevelopmental and cognitive traits. Here, we compiled data from 52 studies involving 4786 rodents (412 effect sizes) to quantify the intergenerational transmission of exercise effects on brain and cognition. Using a multilevel meta-analytic approach, we found that, overall, parental exercise showed a tendency for increasing their offspring's brain structure by 12.7% (albeit statistically non-significant) probably via significantly facilitating neurogenesis (16.5%). Such changes in neural anatomy go in hand with a significant 20.8% improvement in neurobehaviour (improved learning and memory, and reduced anxiety). Moreover, we found parental exercise significantly reduces inter-individual differences (i.e. reduced variance in the treatment group) in progeny's neurobehaviour by 10.2% (coefficient of variation ratio, lnCVR), suggesting the existence of an individual by intervention interaction. The positive effects of exercise are modulated by several covariates (i.e. moderators), such as the exercised parent's sex, offspring's sex, and age, mode of exercise, and exercise timing. In particular, parental forced exercise is more efficient than voluntary exercise at significantly improving offspring neurobehaviour (26.0%) and reducing its variability (14.2%). We observed larger effects when parental exercise started before pregnancy. However, exercising only during pregnancy also had positive effects. Mechanistically, exercise significantly upregulated brain-derived neurotrophic factor (BDNF) by 28.9%, vascular endothelial growth factor (VEGF) by 35.8%, and significantly decreased hippocampal DNA methylation by 3.5%, suggesting that brain growth factor cascades and epigenetic modifications can moderate the transmission of parental exercise effects. Collectively, by coupling mean with variance effects, our analyses draw a more integrated picture of the benefits that parental exercise has on offspring: not only does it improve offspring brain development and cognitive performance, but it also reduces inter-individual differences in cognition-related traits. We advocate that meta-analysis of variation together with the mean of a trait provides novel insights for old controversies as well as emerging new questions, opening up a new era for generating variance-based hypotheses.

Cardiac Effects of Treadmill Running at Different Intensities in a Rat Model

Purpose: In this study, we investigated the effect of treadmill exercise training on cardiac hypertrophy, collagen deposition, echo parameters and serum levels of cardiac troponin I (cTnI) in rats, and how they differ with various exercise intensities, hence exploring potential signal transduction. Methods: Male Sprague-Dawley rats were randomly divided into sedentary (SED), low-intensity running (LIR), medium-intensity running (MIR), and high-intensity running (HIR) groups. Each exercise group had 3 subgroups that were sacrificed for cardiac tissue analyses at 1, 4, and 8 weeks, respectively, and all rats participated in a daily 1 h treadmill routine 5 days per week. Echocardiographic measurements were performed 24 h after the last exercise session. Additionally, myocardium samples and blood were collected for histological and biochemical examinations. Changes in the extracellular signal-regulated kinases 1/2 (ERK1/2) signal pathway were detected by Western blotting. Results: After a week of running, ventricular myocyte size and the phosphorylation of ERK1/2 increased in the HIR group, while left ventricular (LV) diastolic diameter values and LV relative wall thickness increased in the LIR and MIR groups. In addition, we observed heart enlargement, cTnI decrease, and ERK1/2 signal activation in each of the exercise groups after 4 weeks of running. However, the HIR group displayed substantial rupture and increased fibrosis in myocardial tissue. In addition, compared with the LIR and MIR groups, 8 weeks of HIR resulted in structural damage, fiber deposition, and increased cTnI. However, there was no difference in the activation of ERK1/2 signaling between the exercise and SED groups. Conclusion: The effect of running on cardiac hypertrophy was intensity dependent. In contrast to LIR and MIR, the cardiac hypertrophy induced by 8 weeks of HIR was characterized by potential cardiomyocyte injury, which increased the risk of pathological development. Furthermore, the ERK signaling pathway was mainly involved in the compensatory hypertrophy process of the myocardium in the early stage of exercise and was positively correlated with exercise load. However, long-term exercise may attenuate ERK signaling activation.

Time-course of running treadmill adaptation in novice treadmill runners

Studies on running biomechanics and energetics are usually conducted on a treadmill. To ensure that locomotion on a treadmill is comparable to locomotion overground, participants need to be expert in the use of the device. This study aimed to identify the number and duration of sessions needed to obtain stable measurements for spatiotemporal and metabolic parameters in unexperienced treadmill runners. Fourteen male recreational runners performed three 15-min treadmill running trials in different days at a submaximal speed. Spatiotemporal and metabolic parameters were registered at minutes: 5, 10, 15 and their within-trial and between-trial changes were analysed using a two-way repeated measures ANOVA and Bonferroni post-hoc test. Within-trial differences were found in step frequency (decreased over time), Step Length and Contact Time (increased), reaching stability at different time points. Ventilator parameters increased, reaching stability after 5-10 min, while heart rate increased progressively over time. The only between-trial differences were an increase in step length and a decrease in step frequency at min 1, between trials 1 and 3. In conclusion, at least three running trials of 15 min are required to familiarize with the device. The last 5 min of the third trial can be regarded as stable measurements.

Acute bout of exercise downregulates thioredoxin-interacting protein expression in rat contracting skeletal muscles

We previously reported that in rat skeletal muscle, disuse (i.e., decreased muscle contractile activity) rapidly increases thioredoxin-interacting protein (TXNIP), which is implicated in the reduced glucose uptake. Accordingly, we sought herein to (a) determine the effect of exercise (i.e., increased muscle contractile activity) on muscle TXNIP protein expression, and (b) elucidate the mechanisms underlying the changes of TXNIP protein expression in response to exercise. Rat epitrochlearis and soleus muscles were dissected out after an acute bout of 3-hr swimming (without weight loading) or 3-hr treadmill running (15% grade at 9m/min). In a separate protocol, the isolated epitrochlearis and soleus muscles were incubated for 3 hr with AMP-dependent protein kinase activator AICAR. Immediately after the cessation of the 3-hr swimming, the TXNIP protein was decreased in epitrochlearis but not in soleus muscle. Conversely, 3-hr treadmill running decreased the TXNIP protein in soleus but not in epitrochlearis muscle. TXNIP protein was decreased concomitantly with reduced postexercise muscle glycogen, showing that a decrease in TXNIP protein expression occurs in muscles that are recruited during exercise. In addition, 3-hr incubation with AICAR decreased TXNIP protein in both isolated epitrochlearis and soleus muscles. Our results suggest that (a) an acute bout of exercise downregulates TXNIP protein expression in rat contracting skeletal muscles, and (b) the reduction in TXNIP protein expression in contracting muscles is probably mediated by AMPK activation, at least in part.

Parvalbumin Interneuron Activation-Dependent Adult Hippocampal Neurogenesis Is Required for Treadmill Running to Reverse Schizophrenia-Like Phenotypes

Physical exercise can alleviate some of the schizophrenia symptoms in patients, the mechanisms, however, are still unclear. To investigate whether the GABAergic interneuron involved in the therapeutic effect of treadmill running on schizophrenia, the parvalbumin (PV)-positive GABAergic interneurons in the dentate gyrus (DG) was specifically activated or abolished and the effects were evaluated. In the MK801-induced schizophrenia-like animal model, we found:(1) Treadmill running rescued the schizophrenia-related behavioral phenotypes, promoted the adult hippocampal neurogenesis, and increased the dendrite number and complexity of newborn neurons. (2) Treadmill running increased the number of PV-positive interneurons in the DG; genetic ablation of these interneurons reduced adult neurogenesis and abolished the effect of treadmill running on the schizophrenia-related behaviors. Consistently, chemogenetic activation of these interneurons improved neurogenesis and alleviated the schizophrenia-related behaviors. These results suggest a pivotal role of PV-positive interneuron-mediated adult neurogenesis in exercise. (3) However, schizophrenia-related behavioral phenotypes and adult neurogenesis in the DG could still be reversed by exercise after specifically knocking out the schizophrenia-related gene ErbB4 in PV interneurons, as a means to reduce their GABA release. These results suggest that activation of PV interneurons in the DG is sufficient for treadmill running to reverse schizophrenia-like phenotypes.

The effect of preventive exercise on the neuroprotection in 6-hydroxydopamine-lesioned rat brain

Parkinson's disease is characterized by neurodegeneration and learning deficiency. Physical exercise can alleviate these symptoms by increasing the expression of some effective and relevant factors. The preventive effect of 16-week treadmill running in a rat model of Parkinson's disease, before 6-hydroxydopamine (6-OHDA) induction, was assessed. Experimental groups consisted of sedentary (SED), SED+6-OHDA, exercised (EX), and EX+6-OHDA rats. Forty-eight hours after the last session of exercise, 6-OHDA was injected into the medial forebrain bundle (MFB). One week after the injection, behavioral tests, including spatial learning and memory, were assessed through Morris water maze (MWM) and apomorphine-induced rotation. Three weeks after the injection, mRNA expression and protein levels of the transcriptional co-activator peroxisome-proliferator-activated receptor-γ co-activator-1α (PGC-1α), fibronectin type III domain-containing protein 5 (FNDC5), brain-derived neurotrophic factor (BDNF), and tyrosine hydroxylase (TH) were measured in the striatum and the hippocampus of rats by applying real-time PCR and Western blotting. The findings indicate that exposure to 6-OHDA leads to impairments in behavioral and molecular functions. Exercise training prevents and reduces the symptoms caused by dopamine toxins. The results suggest that treadmill running can exert neuroprotective and have preventive effects to reduce Parkinson's disease symptoms. Novelty Parkinson's disease impairs spatial learning and memory. Parkinson's disease reduced levels of PGC-1α, FNDC5, and BDNF and increased neurodegeneration in the striatum and the hippocampus. Treadmill running before disease attenuated 6-OHDA-induced memory deficit and elevated neuroprotection. Exercise has multiple effects on memory and biochemical factors.

Development of a Mouse Model of Knee Osteoarthritis Based on Obesity and Bipedal Walking

To investigate the influence of obesity and obligatory bipedal walking on osteoarthritis (OA) development, 26-week-old C57BL/6 mice were divided into two groups and obesity was induced in one group with a 60% fat diet. After 8 weeks, mice from each group were again divided into two groups and obligatory bipedal exercise was induced with a specially designed treadmill in one group, resulting in four experimental groups (control, control bipedal, obese, and obese bipedal). After 8, 10, and 12 weeks of bipedal walking, knee joints were obtained and graded. Surface fibrillation and matrix proteoglycan depletion, began to appear after 8 weeks of exercise in the bipedal groups and progressed as the duration of the exercise increased. At 12 weeks, cartilage loss extending >75% of articular cartilage was observed in none of the control and obese groups, and in 42.8% and 77.7% of control bipedal and obese bipedal animals, respectively. OA grading was significantly higher in the obese bipedal group compared with the control bipedal group. The von Frey fiber test thresholds decreased significantly in the bipedal groups compared with the control and obese groups. This model can be used to study the pathogenesis of human OA and to evaluate its therapeutic agents. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2411-2419, 2019.

Influence of the Size of the Field of View on Visual Perception While Running in a Treadmill-Mediated Virtual Environment

We investigated how the size of the horizontal field of view (FoV) affects visual speed perception with individuals running on a treadmill. Twelve moderately trained to trained participants ran on a treadmill at two different speeds (8 and 12 km/h) in front of a moving virtual scene. Different masks were used to manipulate the visible visual field, masking either the central or the peripheral area of the virtual scene or showing the full visual field. We asked participants to match the visual speed of the scene to their actual running speed. For each trial, participants indicated whether the scene was moving faster or slower than they were running. Visual speed was adjusted according to the responses using a staircase method until the Point of Subjective Equality was reached, that is until visual and running speed were perceived as matching. For both speeds and all FoV conditions, participants underestimated visual speed relative to the actual running speed. However, this underestimation was significant only when the peripheral FoV was masked. These results confirm that the size of the FoV should absolutely be taken into account for the design of treadmill-mediated virtual environments (VEs).

Treadmill Running in Established Phase Arthritis Inhibits Joint Destruction in Rat Rheumatoid Arthritis Models

Exercise therapy inhibits joint destruction by suppressing pro-inflammatory cytokines. The efficacy of pharmacotherapy for rheumatoid arthritis differs depending on the phase of the disease, but that of exercise therapy for each phase is unknown. We assessed the differences in the efficacy of treadmill running on rheumatoid arthritis at various phases, using rat rheumatoid arthritis models. Rats with collagen-induced arthritis were used as rheumatoid arthritis models, and the phase after immunization was divided as pre-arthritis and established phases. Histologically, the groups with forced treadmill running in the established phase had significantly inhibited joint destruction compared with the other groups. The group with forced treadmill running in only the established phase had significantly better bone morphometry and reduced expression of connexin 43 and tumor necrosis factor α in the synovial membranes compared with the no treadmill group. Furthermore, few cells were positive for cathepsin K immunostaining in the groups with forced treadmill running in the established phase. Our results suggest that the efficacy of exercise therapy may differ depending on rheumatoid arthritis disease activity. Active exercise during phases of decreased disease activity may effectively inhibit arthritis and joint destruction.

A Single Session of Aerobic Exercise Mediates Plasticity-Related Phosphorylation in both the Rat Motor Cortex and Hippocampus

A single session of aerobic exercise may offer one means to "prime" motor regions to be more receptive to the acquisition of a motor skill; however, the mechanisms whereby this priming may occur are not clear. One possible explanation may be related to the post-translational modification of plasticity-related receptors and their associated intracellular signaling molecules, given that these proteins are integral to the development of synaptic plasticity. In particular, phosphorylation governs the biophysical properties (e.g., Ca²⁺ conductance) and the migratory patterns (i.e., trafficking) of plasticity-related receptors by altering the relative density of specific receptor subunits at synapses. We hypothesized that a single session of exercise would alter the subunit phosphorylation of plasticity-related receptors (AMPA receptors, NMDA receptors) and signaling molecules (PKA, CaMKII) in a manner that would serve to prime motor cortex. Young, male Sprague-Dawley rats (n = 24) were assigned to either exercise (Moderate, Exhaustion), or non-exercising (Sedentary) groups. Immediately following a single session of treadmill exercise, whole tissue homogenates were prepared from both the motor cortex and hippocampus. We observed a robust (1.2-2.0× greater than sedentary) increase in tyrosine phosphorylation of AMPA (GluA1,2) and NMDA (GluN2A,B) receptor subunits, and a clear indication that exercise preferentially affects pPKA over pCaMKII. The changes were found, specifically, following moderate, but not maximal, acute aerobic exercise in both motor cortex and hippocampus. Given the requirement for these proteins during the early phases of plasticity induction, the possibility exists that exercise-induced priming may occur by altering the phosphorylation of plasticity-related proteins.

Effects of prostate cancer and exercise training on left ventricular function and cardiac and skeletal muscle mass

Prostate cancer was found to reduce cardiac and left ventricle (LV) masses in association with diminished exercise capacity in rats. We tested the hypothesis that exercise training will mitigate prostate cancer-induced cardiac and skeletal muscle atrophy and improve LV function versus sedentary tumor-bearing counterparts. Copenhagen rats ( n = 39; ~5 mo old) were randomized into four groups: exercise-trained tumor-bearing (EXTB) or control (EXCON) and sedentary tumor-bearing (SEDTB) or control (SEDCON). Dunning R-3327 prostate cancer cells were injected orthotopically in 19 of the 39 animals. Treadmill exercise training was performed for 60 min/day for ~30 days. Animals underwent echocardiography to examine ventricle dimensions "Pre-" cancer injection or exercise (PRE) and 15 (Post 1) and 32-35 (Post 2) days after cancer cell injection with tissues collected after Post 2. LV TNF-α and IL-6 concentrations were measured post mortem. Cardiac and LV mass of SEDTB animals were lower than all groups ( P < 0.05). Tumor mass was negatively correlated with LV mass in EXTB (-0.75, P < 0.02) and SEDTB animals (-0.72, P < 0.02). EXCON group had higher stroke volume Post 2 assessment compared with both sedentary groups ( P < 0.05) but not EXTB animals. No difference in LV [IL-6] or [TNF-α] was found between the cancer groups. The current investigation demonstrates prostate cancer, independent of anticancer treatment, significantly reduces cardiac mass and LV mass as well as locomotor muscle masses. However, moderate-intensity exercise training can mitigate cardiac and skeletal muscle atrophy with prostate cancer and preserve the cardiac phenotype (i.e., mass and function) to that of the healthy sedentary group. NEW & NOTEWORTHY This study demonstrates the atrophic effects of prostate cancer on cardiac and skeletal muscle mass independent of anticancer treatment(s) that can be mitigated with moderate-intensity exercise. These findings have important implications for potentially improving the quality of life as well as therapeutic outcomes for patients with prostate cancer.

Endurance exercise training does not limit coronary atherosclerosis in familial hypercholesterolemic swine

Human studies demonstrate that physical activity reduces both morbidity and mortality of coronary heart disease (CHD) including decreased progression and/or regression of CHD with life-style modification which includes exercise. However, evidence supporting an intrinsic, direct effect of exercise in attenuating the development of CHD is equivocal. One limitation has been the lack of a large animal model with clinically evident CHD disease. Thus, we examined the role of endurance exercise in CHD development in a swine model of familial hypercholesterolemia (FH) that exhibits robust, complex atherosclerosis. FH swine were randomly assigned to either sedentary (Sed) or exercise trained (Ex) groups. At 10 months of age, Ex pigs began a 10 months, moderate-intensity treadmill-training intervention. At 14 months, all pigs were switched to a high-fat, high-cholesterol diet. CHD was assessed by intravascular ultrasound (IVUS) both prior to and after completion of 6 months on the HFC diet. Prior to HFC diet, Ex resulted in a greater coronary artery size in the proximal and mid sections of the LCX compared to SED, with no effect in the LAD. After 6 months on HFC diet, there was a 5-6 fold increase in absolute plaque volume in all segments of the LCX and LAD in both groups. At 20 months, there was no difference in vessel volume, lumen volume, absolute or relative plaque volume in either the LCX or LAD between Sed and Ex animals. These findings fail to support an independent, direct effect of exercise in limiting CHD progression in familial hypercholesterolemia.

Paternal physical exercise modulates global DNA methylation status in the hippocampus of male rat offspring

It is widely known that maternal physical exercise is able to induce beneficial improvements in offspring cognition; however, the effects of paternal exercise have not been explored in detail. The present study was designed to evaluate the impact of paternal physical exercise on memory and learning, neuroplasticity and DNA methylation levels in the hippocampus of male offspring. Adult male Wistar rats were divided into two groups: sedentary or exercised fathers. The paternal preconception exercise protocol consisted of treadmill running, 20 minutes daily, 5 consecutive days per week for 22 days, while the mothers were not trained. After mating, paternal sperm was collected for global DNA methylation analysis. At postnatal day 53, the offspring were euthanized, and the hippocampus was dissected to measure cell survival by 5-bromo-2′-deoxiuridine and to determine the expression of synaptophysin, reelin, brain-derived neurotrophic factor and global DNA methylation levels. To measure spatial memory and learning changes in offspring, the Morris water maze paradigm was used. There was an improvement in spatial learning, as well as a significant decrease in hippocampal global DNA methylation levels in the offspring from exercised fathers compared with those from sedentary ones; however, no changes were observed in neuroplasticity biomarkers brain-derived neurotrophic factor, reelin and 5-bromo-2′-deoxiuridine. Finally, the global DNA methylation of paternal sperm was not significantly changed by physical exercise. These results suggest a link between paternal preconception physical activity and cognitive benefit, which may be associated with hippocampal epigenetic programming in male offspring. However, the biological mechanisms of this modulation remain unclear.

Exercise Training Impacts Cardiac Mitochondrial Proteome Remodeling in Murine Urothelial Carcinoma

Cardiac dysfunction secondary to cancer may exert a negative impact in patients’ tolerance to therapeutics, quality of life, and survival. The aim of this study was to evaluate the potential therapeutic effect of exercise training on the heart in the setting of cancer, after diagnosis. Thus, the molecular pathways harbored in heart mitochondria from a murine model of chemically-induced urothelial carcinoma submitted to 8-weeks of high intensity treadmill exercise were characterized using mass spectrometry-based proteomics. Data highlight the protective effects of high intensity exercise training in preventing left ventricle diastolic dysfunction, fibrosis, and structural derangement observed in tumor-bearing mice. At the mitochondrial level, exercise training counteracted the lower ability to produce ATP observed in the heart of animals with urothelial carcinoma and induced the up-regulation of fatty acid oxidation and down-regulation of the biological process “cardiac morphogenesis”. Taken together, our data support the prescription of exercise training after cancer diagnosis for the management of disease-related cardiac dysfunction.

Fat and Lean Mass Predict Bone Mass During Energy Restriction in Sedentary and Exercising Rodents

Energy restriction (ER) causes bone loss, but the impact of exercise during ER is less understood. In this study, we examined the impact of metabolic hormones and body composition on both total body bone mineral content (BMC) and local (proximal tibia) volumetric bone mineral density (vBMD) during short- (4 weeks) and long-term (12 weeks) ER with and without exercise in adult female rats. Our first goal was to balance energy between sedentary and exercising groups to determine the impact of exercise during ER. Second, we aimed to determine the strongest predictors of bone outcomes during ER with energy-matched exercising groups.

Methods: Female Sprague–Dawley rats were divided into three sedentary groups (ad libitum, –20% ER, and –40% ER) and three exercising groups (ad libitum, –10% ER, and –30% ER). Approximately a 10% increase in energy expenditure was achieved via moderate treadmill running (∼60–100 min 4 days/week) in EX groups. n per group = 25–35. Data were analyzed as a 2 × 3 ANOVA with multiple linear regression to predict bone mass outcomes.

Results: At 4 weeks, fat and lean mass and serum insulin-like growth factor-I (IGF-I) predicted total body BMC (R² = 0.538). Fat mass decreased with ER at all levels, while lean mass was not altered. Serum IGF-I declined in the most severe ER groups (–40 and –30%). At 12 weeks, only fat and lean mass predicted total body BMC (R² = 0.718). Fat mass declined with ER level regardless of exercise status and lean mass increased due to exercise (+5.6–6.7% vs. energy-matched sedentary groups). At the same time point, BMC declined with ER, but increased with exercise (+7.0–12.5% vs. energy-matched sedentary groups). None of our models predicted vBMD at the proximal tibia at either time point.

Conclusion: Both fat and lean mass statistically predicted total body BMC during both short- and long-term ER. Fat and lean mass decreased with ER, while lean mass increased with EX at each energy level. Measures that predicted total body skeletal changes did not predict site-specific changes. These data highlight the importance of maintaining lean mass through exercise during periods of ER.

Upper Trunk-Pelvis Coordination During Running Using the Continuous Relative Fourier Phase Method

The upper trunk-pelvic coordination patterns used in running are not well understood. The purposes of this study are to (1) test the running speed effect on the upper trunk-pelvis axial rotation coordination and (2) present a step-by-step guide of the relative Fourier phase algorithm, as well as some further issues to consider. A total of 20 healthy young adults were tested under 3 treadmill running speeds using a 3-dimensional motion capture system. The upper trunk and pelvic segmental angles in axial rotation were calculated, and the coordination was quantified using the relative Fourier phase method. Results of multilevel modeling indicated that running speed did not significantly contribute to the changes in coordination in a linear pattern. A qualitative template analysis suggested that participants displayed different change patterns of coordination as running speed increased. Participants did not significantly change the upper trunk and pelvis coordination mode in a linear pattern at higher running speeds, possibly because they employed different motion strategies to achieve higher running speeds and thus displayed large interparticipant variations. For most of our runners, running at a speed deviated from the preferred speed could alter the upper trunk-pelvis coordination. Future studies are still needed to better understand the influence of altered coordination on running performance and injuries.

Treadmill Running Ameliorates Destruction of Articular Cartilage and Subchondral Bone, Not Only Synovitis, in a Rheumatoid Arthritis Rat Model

We analyzed the influence of treadmill running on rheumatoid arthritis (RA) joints using a collagen-induced arthritis (CIA) rat model. Eight-week-old male Dark Agouti rats were randomly divided into four groups: The control group, treadmill group (30 min/day for 4 weeks from 10-weeks-old), CIA group (induced CIA at 8-weeks-old), and CIA + treadmill group. Destruction of the ankle joint was evaluated by histological analyses. Morphological changes of subchondral bone were analyzed by μ-CT. CIA treatment-induced synovial membrane invasion, articular cartilage destruction, and bone erosion. Treadmill running improved these changes. The synovial membrane in CIA rats produced a large amount of tumor necrosis factor-α and Connexin 43; production was significantly suppressed by treadmill running. On μ-CT of the talus, bone volume fraction (BV/TV) was significantly decreased in the CIA group. Marrow star volume (MSV), an index of bone loss, was significantly increased. These changes were significantly improved by treadmill running. Bone destruction in the talus was significantly increased with CIA and was suppressed by treadmill running. On tartrate-resistant acid phosphate and alkaline phosphatase (TRAP/ALP) staining, the number of osteoclasts around the pannus was decreased by treadmill running. These findings indicate that treadmill running in CIA rats inhibited synovial hyperplasia and joint destruction.

Effect on intensity of treadmill running on learning, memory and expressions of cell cycle-related proteins in rats with cerebral ischemia

Objective

We discussed the intensity of treadmill running on learning, memory and expression of cell cycle-related proteins in rats with cerebral ischemia.

Method

Eighty healthy male SD rats were randomly divided into normal group, model group, intensity I group and intensity II group, with 20 rats in each group. The four-vessel occlusion method of Pulsinelli (4-VO) was used to induce global cerebral ischemia. Brain neuronal morphology was observed by hematoxylin-eosin (HE) staining at 3h, 6h, 24h and 48h after modeling, respectively. Hippocampal expressions of cyclin A and cyclin E were detected by immunohistochemistry. At 48h after modeling, the learning and memory performance of rats was tested by water maze experiment.

Result

Compared with the normal group, the other three groups had a significant reduction in surviving neurons, prolonging of escape latency and decreased number of passes over the former position of the platform (P<0.05). The number of surviving neurons and the number of passes over the former position of the platform were obviously lower in the model group than in intensity I group (P<0.05), but significantly higher compared with intensity II group (P<0.05). Escape latency of the model group was obviously prolonged as compared with intensity I group (P<0.05), but much shorter than that of intensity II group (P<0.05). Compared with the normal group, the expressions of cyclin A and cyclin E were significantly upregulated at different time points after modeling (P<0.05). The expression of the model group was higher than that of intensity I group, but lower than that of intensity II group (P<0.05).

Conclusion

Moderate intensity of treadmill running can help protect brain neurons and improve learning and memory performance of rats with global cerebral ischemia. But high intensity of treadmill running has a negative impact, possibly through the regulation of cell cycle-related proteins in ischemia/reperfusion injury.

Mechanobiology of young and aging tendons: In vivo studies with treadmill running

Tendons are unique in the sense that they are constantly subjected to large mechanical loads and that they contain tendon-specific cells, including tenocytes and tendon stem/progenitor cells. The responses of these cells to mechanical loads can be anabolic or catabolic and as a result, change the biological properties of the tendon itself that may be beneficial or detrimental. On the other hand, aging also induces aberrant changes in cellular expression of various genes and production of various types of matrix proteins in the tendon, and consequently lead to tendon degeneration and impaired healing in aging tendons; both could be improved by moderate physiological mechanical loading such as treadmill running. This article gives an overview on the mechanobiology research of young and aging animal tendons using treadmill running model. The challenges in such treadmill running studies are also discussed. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:557-565, 2018.

Differences in Exercise Capacity and Responses to Training in 24 Inbred Mouse Strains

Changes in cardiorespiratory fitness in response to a standardized exercise training protocol differ substantially between individuals. Results from cross-sectional, twin, and family studies indicate genetics contribute to individual differences in both baseline exercise capacity and the response to training. Exercise capacity and responses to training also vary between inbred strains of mice. However, such studies have utilized a limited number of inbred strains. Therefore, the aim of this study was to characterize exercise-training responses in a larger number of genetically diverse strains of inbred mice and estimate the contribution of genetic background to exercise training responses. Eight-week old male mice from 24 inbred strains (n = 4–10/strain) performed a graded exercise test before and after 4 weeks of exercise training. Before training, exercise capacity was significantly different between strains when expressed as time (range = 21–42 min) and work performed (range = 0.42–3.89 kg·m). The responses to training also were significantly different between strains, ranging from a decrease of 2.2 min in NON/ShiLtJ mice to an increase of 8.7 min in SWR/J mice. Changes in work also varied considerably between the lowest (−0.24 kg·m in NON/ShiLtJ) and highest (+2.30 kg·m in FVB/NJ) performing strains. Heart and skeletal muscle masses also varied significantly between strains. Two broad sense heritability estimates were calculated for each measure of exercise capacity and for responses to training. For change in run time, the intraclass correlation between mice within the same inbred strain (r_I) was 0.58 and the coefficient of genetic determination (g²) was 0.41. Heritability estimates were similar for the change in work: r_I = 0.54 and g² = 0.37. In conclusion, these results indicate genetic background significantly influences responses to exercise training.

Effects of mild running on substantia nigra during early neurodegeneration

Moderate physical exercise acts at molecular and behavioural levels, such as interfering in neuroplasticity, cell death, neurogenesis, cognition and motor functions. Therefore, the aim of this study is to analyse the cellular effects of moderate treadmill running upon substantia nigra during early neurodegeneration. Aged male Lewis rats (9-month-old) were exposed to rotenone 1mg/kg/day (8 weeks) and 6 weeks of moderate treadmill running, beginning 4 weeks after rotenone exposure. Substantia nigra was extracted and submitted to proteasome and antioxidant enzymes activities, hydrogen peroxide levels and Western blot to evaluate tyrosine hydroxylase (TH), alpha-synuclein, Tom-20, PINK1, TrkB, SLP1, CRMP-2, Rab-27b, LC3II and Beclin-1 level. It was demonstrated that moderate treadmill running, practiced during early neurodegeneration, prevented the increase of alpha-synuclein and maintained the levels of TH unaltered in substantia nigra of aged rats. Physical exercise also stimulated autophagy and prevented impairment of mitophagy, but decreased proteasome activity in rotenone-exposed aged rats. Physical activity also prevented H₂O₂ increase during early neurodegeneration, although the involved mechanism remains to be elucidated. TrkB levels and its anterograde trafficking seem not to be influenced by moderate treadmill running. In conclusion, moderate physical training could prevent early neurodegeneration in substantia nigra through the improvement of autophagy and mitophagy.

Exercise training with concomitant nitric oxide synthase inhibition improved anxiogenic behavior, spatial cognition, and BDNF/P70S6 kinase activation in 20-month-old rats

This study aimed to investigate the effect of exercise and nitric oxide synthase (NOS) inhibition on memory, anxiety, and protein levels of brain-derived neurotrophic factor (BDNF) and P70S6 kinase (P70S6K). Twenty-month-old rats were divided into 6 groups: a control group, 2 groups treated with l-nitro-arginine methyl ester (L-NAME) (25 or 100 mg/kg) for 63 days, 2 groups treated with L-NAME (25 or 100 mg/kg) for 63 days plus 2 months of exercise, and 1 group treated with exercise. Behavioral tests were conducted to determine the anxiolytic and memory-improving role of exercise and NOS inhibition. BDNF, P70S6K, and cleaved caspase-3 protein levels in the hippocampus and prefrontal cortex were evaluated by Western blotting. Exercise and L-NAME (25 mg/kg) or their combination had an anxiolytic effect and improved spatial memory in old rats compared with the control or exercised group, respectively. Exercise and treatment with a low dose of L-NAME (25 mg/kg) each increased BDNF and P70S6K in the hippocampus and prefrontal cortex compared with levels in control rats. In comparison with exercise alone, co-treatment with exercise and a low dose of L-NAME (25 mg/kg) also increased BDNF and P70S6K in the hippocampus. The neuronal level of cleaved caspase-3 was reduced in the L-NAME (25 mg/kg) + exercise group compared with the exercised group. The L-NAME (100 mg/kg) + exercise treatment had no positive behavioral or molecular effects compared with exercise alone. The protective role of NOS inhibition and aerobic exercise against aging is probably modulated via BDNF and P70S6K in the brain.

Maximal Oxygen Uptake Is Achieved in Hypoxia but Not Normoxia during an Exhaustive Severe Intensity Run

Highly aerobically trained individuals are unable to achieve maximal oxygen uptake (V˙O2max) during exhaustive running lasting ~2 min, instead V˙O2 plateaus below V˙O2max after ~1 min. Hypoxia offers the opportunity to study the (V˙O2) response to an exhaustive run relative to a hypoxia induced reduction in V˙O2max. The aim of this study was to explore whether there is a difference in the percentage of V˙O2max achieved (during a 2 min exhaustive run) in normoxia and hypoxia. Fourteen competitive middle distance runners (normoxic V˙O2max 67.0 ± 5.2 ml.kg⁻¹.min⁻¹) completed exhaustive treadmill ramp tests and constant work rate (CWR) tests in normoxia and hypoxia (F_iO₂ 0.13). The V˙O2 data from the CWR tests were modeled using a single exponential function. End exercise normoxic CWR V˙O2 was less than normoxic V˙O2max (86 ± 6% ramp, P < 0.001). During the hypoxic CWR test, hypoxic V˙O2max was achieved (102 ± 8% ramp, P = 0.490). The phase II time constant was greater in hypoxia (12.7 ± 2.8 s) relative to normoxia (10.4 ± 2.6 s) (P = 0.029). The results demonstrate that highly aerobically trained individuals cannot achieve V˙O2max during exhaustive severe intensity treadmill running in normoxia, but can achieve the lower V˙O2max in hypoxia despite a slightly slower V˙O2 response.

Moderate treadmill running exercise prior to tendon injury enhances wound healing in aging rats

The effect of exercise on wound healing in aging tendon was tested using a rat moderate treadmill running (MTR) model. The rats were divided into an MTR group that ran on a treadmill for 4 weeks and a control group that remained in cages. After MTR, a window defect was created in the patellar tendons of all rats and wound healing was analyzed. We found that MTR accelerated wound healing by promoting quicker closure of wounds, improving the organization of collagen fibers, and decreasing senescent cells in the wounded tendons when compared to the cage control. MTR also lowered vascularization, increased the numbers of tendon stem/progenitor cells (TSCs) and TSC proliferation than the control. Besides, MTR significantly increased the expression of stem cell markers, OCT-4 and Nanog, and tenocyte genes, Collagen I, Collagen III and tenomodulin, and down-regulated PPAR-γ, Collagen II and Runx-2 (non-tenocyte genes). These findings indicated that moderate exercise enhances healing of injuries in aging tendons through TSC based mechanisms, through which exercise regulates beneficial effects in tendons. This study reveals that appropriate exercise may be used in clinics to enhance tendon healing in aging patients.

Chronic stress-induced memory deficits are reversed by regular exercise via AMPK-mediated BDNF induction

Chronic stress has a detrimental effect on neurological insults, psychiatric deficits, and cognitive impairment. In the current study, chronic stress was shown to impair learning and memory functions, in addition to reducing in hippocampal Adenosine monophosphate-activated protein kinase (AMPK) activity. Similar reductions were also observed for brain-derived neurotrophic factor (BDNF), synaptophysin, and post-synaptic density-95 (PSD-95) levels, all of which was counter-regulated by a regime of regular and prolonged exercise. A 21-day restraint stress regimen (6 h/day) produced learning and memory deficits, including reduced alternation in the Y-maze and decreased memory retention in the water maze test. These effects were reversed post-administration by a 3-week regime of treadmill running (19 m/min, 1 h/day, 6 days/week). In hippocampal primary culture, phosphorylated-AMPK (phospho-AMPK) and BDNF levels were enhanced in a dose-dependent manner by 5-amimoimidazole-4-carboxamide riboside (AICAR) treatment, and AICAR-treated increase was blocked by Compound C. A 7-day period of AICAR intraperitoneal injections enhanced alternation in the Y-maze test and reduced escape latency in water maze test, along with enhanced phospho-AMPK and BDNF levels in the hippocampus. The intraperitoneal injection of Compound C every 4 days during exercise intervention diminished exercise-induced enhancement of memory improvement during the water maze test in chronically stressed mice. Also, chronic stress reduced hippocampal neurogenesis (lower Ki-67- and doublecortin-positive cells) and mRNA levels of BDNF, synaptophysin, and PSD-95. Our results suggest that regular and prolonged exercise can alleviate chronic stress-induced hippocampal-dependent memory deficits. Hippocampal AMPK-engaged BDNF induction is at least in part required for exercise-induced protection against chronic stress.

Improvements in impaired GABA and GAD65/67 production in the spinal dorsal horn contribute to exercise-induced hypoalgesia in a mouse model of neuropathic pain

Background

Physical exercise effectively attenuates neuropathic pain, and multiple events including the inhibition of activated glial cells in the spinal dorsal horn, activation of the descending pain inhibitory system, and reductions in pro-inflammatory cytokines in injured peripheral nerves may contribute to exercise-induced hypoalgesia. Since fewer GABAergic hypoalgesic interneurons exist in the dorsal horn in neuropathic pain model animals, the recovery of impaired GABAergic inhibition in the dorsal horn may improve pain behavior. We herein determined whether the production of gamma-aminobutyric acid (GABA) and glutamic acid decarboxylase (GAD) in the dorsal horn is restored by treadmill running and contributes to exercise-induced hypoalgesia in neuropathic pain model mice. C57BL/6 J mice underwent partial sciatic nerve ligation (PSL). PSL-Runner mice ran on a treadmill at 7 m/min for 60 min/day, 5 days/week, from two days after PSL.

Results

Mechanical allodynia and heat hyperalgesia developed in PSL-Sedentary mice but were significantly attenuated in PSL-Runner mice. PSL markedly decreased GABA and GAD65/67 levels in neuropils in the ipsilateral dorsal horn, while treadmill running inhibited these reductions. GABA+ neuronal nuclei+ interneuron numbers in the ipsilateral dorsal horn were significantly decreased in PSL-Sedentary mice but not in PSL-Runner mice. Pain behavior thresholds positively correlated with GABA and GAD65/67 levels and GABAergic interneuron numbers in the ipsilateral dorsal horns of PSL-Sedentary and -Runner mice.

Conclusions

Treadmill running prevented PSL-induced reductions in GAD65/67 production, and, thus, GABA levels may be retained in interneurons and neuropils in the superficial dorsal horn. Therefore, improvements in impaired GABAergic inhibition may be involved in exercise-induced hypoalgesia.

Thermoregulatory responses in exercising rats: methodological aspects and relevance to human physiology

Rats are used worldwide in experiments that aim to investigate the physiological responses induced by a physical exercise session. Changes in body temperature regulation, which may affect both the performance and the health of exercising rats, are evident among these physiological responses. Despite the universal use of rats in biomedical research involving exercise, investigators often overlook important methodological issues that hamper the accurate measurement of clear thermoregulatory responses. Moreover, much debate exists regarding whether the outcome of rat experiments can be extrapolated to human physiology, including thermal physiology. Herein, we described the impact of different exercise intensities, durations and protocols and environmental conditions on running-induced thermoregulatory changes. We focused on treadmill running because this type of exercise allows for precise control of the exercise intensity and the measurement of autonomic thermoeffectors associated with heat production and loss. Some methodological issues regarding rat experiments, such as the sites for body temperature measurements and the time of day at which experiments are performed, were also discussed. In addition, we analyzed the influence of a high body surface area-to-mass ratio and limited evaporative cooling on the exercise-induced thermoregulatory responses of running rats and then compared these responses in rats to those observed in humans. Collectively, the data presented in this review represent a reference source for investigators interested in studying exercise thermoregulation in rats. In addition, the present data indicate that the thermoregulatory responses of exercising rats can be extrapolated, with some important limitations, to human thermal physiology.

Regular exercise improves cardiac contractile activation by modulating MHC isoforms and SERCA activity in orchidectomized rats

Data from the trial known as Testosterone in Older Men with Mobility Limitations (TOM) has indicated an association between testosterone administration and a greater risk for adverse cardiovascular events. We therefore propose that regular exercise is a cardioprotective alternative that prevents detrimental changes in contractile activation when a deficiency in male sex hormones exists. Ten-week-old orchidectomized (ORX) rats were subjected to a 9-wk treadmill running program at moderate intensity starting 1 wk after surgery. Although exercise-induced cardiac hypertrophy was observed both in rats that underwent ORX and sham surgery, regular exercise enhanced cardiac myofilament Ca(2+) sensitivity and myosin light-chain 2 phosphorylation only in rats that underwent a sham operation. Although the rats that had sham surgery and and given exercise exhibited no change in maximum developed tension, regular running prevented the suppression of maximum active tension in the hearts of ORX rats. Regular exercise also prevented a shift in myosin heavy chain (MHC) isoforms toward β-MHC, a reduction in sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA) activity, and an increase in SERCA sensitivity in the hearts of ORX rats. Neither SERCA content nor its modulating component, phospholamban (PLB), was altered by exercise in either sham-operated or ORX rats. However, decreases in the phosphorylated Thr(17) form of PLB and the phosphorylated Thr(287) form of Ca(2+)/calmodulin-dependent kinase II in the hearts of ORX rats were abolished after regular exercise. These results thus support the use of regular running as a cardioprotective alternative to testosterone replacement in hypogonadal conditions.

Physical exercise induces rapid release of small extracellular vesicles into the circulation

Cells secrete extracellular vesicles (EVs) by default and in response to diverse stimuli for the purpose of cell communication and tissue homeostasis. EVs are present in all body fluids including peripheral blood, and their appearance correlates with specific physiological and pathological conditions. Here, we show that physical activity is associated with the release of nano-sized EVs into the circulation. Healthy individuals were subjected to an incremental exercise protocol of cycling or running until exhaustion, and EVs were isolated from blood plasma samples taken before, immediately after and 90 min after exercise. Small EVs with the size of 100-130 nm, that carried proteins characteristic of exosomes, were significantly increased immediately after cycling exercise and declined again within 90 min at rest. In response to treadmill running, elevation of small EVs was moderate but appeared more sustained. To delineate EV release kinetics, plasma samples were additionally taken at the end of each increment of the cycling exercise protocol. Release of small EVs into the circulation was initiated in an early phase of exercise, before the individual anaerobic threshold, which is marked by the rise of lactate. Taken together, our study revealed that exercise triggers a rapid release of EVs with the characteristic size of exosomes into the circulation, initiated in the aerobic phase of exercise. We hypothesize that EVs released during physical activity may participate in cell communication during exercise-mediated adaptation processes that involve signalling across tissues and organs.

Utility of electromyographic fatigue threshold during treadmill running

INTRODUCTION

We investigated 2 different methods for determining muscle fatigue threshold by electromyography (EMG).

METHODS

Thirteen subjects completed an incremental treadmill running protocol for EMG fatigue threshold (EMGFT ) determination based on the critical power concept (EMGFT 1) and the breakpoint in the linear relationship between EMG amplitude and exercise intensity (EMGFT 2). Then, both the EMGFT 1 and EMGFT 2 were tested in a continuous treadmill running protocol. EMG was recorded from the rectus femoris (RF), vastus lateralis (VL), biceps femoris (BF), and lateral gastrocnemius (LG) muscles.

RESULTS

For BF, EMGFT 2 was higher than EMGFT 1, and EMGFT 1 for BF was lower than EMGFT 1 for LG. EMG of RF was higher at EMGFT 2 than at EMGFT 1, and LG EMG was lower at EMGFT 2.

CONCLUSIONS

EMGFT can be determined during a single treadmill running test, and EMGFT 1 may be the most appropriate method to estimate the muscle fatigue threshold during running.