Incremental Treadmill Running Research Articles

Impact of Anaerobic Exercise Integrated Into Regular Training on Experienced Judo Athletes: Running Vs. Repetitive Throws.

Kamandulis, S, Dudėnienė, L, Snieckus, A, Kniubaite, A, Mickevicius, M, Lukonaitiene, I, Venckunas, T, Stasiule, L, and Stasiulis, A. Impact of anaerobic exercise integrated into regular training on experienced judo athletes: running vs. repetitive throws. J Strength Cond Res XX(X): 000-000, 2024-Anaerobic training in high-level athletes is of considerable interest to practitioners aiming to optimize performance. This study compared the impact of interval anaerobic training (IAT) sessions consisting of either high-intensity running or throwing that were performed twice a week together with regular judo training on the anaerobic and aerobic performance of experienced judo athletes. Employing a repeated-measures, counterbalancing, research design, 12 national team judo athletes (7 women and 5 men; mean age, 20.4 ± 0.95 years; mean judo training experience, 13.4 ± 1.4 years; competitive level, black belt first and second Dan) performed each IAT modality for 6 weeks, for a full training cycle of 12 weeks. Assessments of their anaerobic fitness (Cunningham and Faulkner Anaerobic Treadmill Test), sport-specific anaerobic fitness (Special Judo Fitness Test [SJFT]), and aerobic capacity (maximal incremental treadmill running test) were performed before, after 6 weeks, and after 12 weeks of training. The uphill running performance improved by 13.1% over the 12-week period (p = 0.047). Simultaneously, there was a 9.0% improvement in the SJFT index and a 6.9% increase in the number of throws (p = 0.011 and p = 0.017, respectively). Although a trend for throwing drills being more effective than interval sprint running was observed, the interaction effect lacked statistical significance (p = 0.074). Moreover, no substantial changes were noted in aerobic endurance markers. In conclusion, this study suggests that incorporating specific and nonspecific high-intensity drills into a routine training regimen may enhance anaerobic capacity among well-trained judo athletes, potentially leading to favorable competitive outcomes.

Menstrual Cycle Phase has no Influence on Performance-Determining Variables in Endurance-Trained Athletes: The FENDURA Project.

To investigate the effect of the MC and endogenous sex hormone concentrations on performance-determining variables in three distinct MC phases in endurance-trained females. Twenty-one eumenorrheic trained/highly trained endurance athletes completed a standardized test battery during the early follicular phase (EFP), ovulatory phase (OP), and mid-luteal phase (MLP) for either one (n = 7) or two test cycles (n = 14). MC phases were determined using calendar-based counting, urinary ovulation testing, and verified with serum hormone analysis. MCs were retrospectively classified as eumenorrheic or disturbed. Disturbed MCs were excluded from analysis. The test battery consisted of 4-6 x 5-min submaximal stages with stepwise speed increases, a 30-s all-out double-poling ski ergometer test, and a maximal incremental treadmill running test. At a group level, there was no effect of MC phase or the serum concentrations of estrogen and progesterone on peak oxygen uptake (O2peak), oxygen uptake at 4 mmol·L-1 blood lactate concentration, time-to-exhaustion, running economy, or mean 30-s power output (MPO30s). Serum testosterone concentration was positively associated with MPO30s (p = 0.016). Changes in O2peak from EFP to MLP were inconsistent between individuals and across cycles. None of the measured performance-determining variables were influenced by MC phase or serum estrogen or progesterone concentrations. While some individual patterns could be observed, there was no indication that any single MC phase is consistently associated with improved or impaired O2peak on a group level.

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

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. 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. 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). 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.

Influence of puberty on high intensity exercise induced skeletal muscle damage and inflammatory response in sedentary boys

The present investigation examined the influence of age and pubertal transition on magnitude of muscle damage and inflammatory response following high intensity incremental treadmill running till volitional exhaustion in sixty-four sedentary prepubertal (n ​= ​32) and postpubertal (n ​= ​32) boys who were randomly recruited in the study. Muscle damage and inflammatory markers like creatine kinase (CK), lactate dehydrogenase (LDH), alanine aminotransferase (ALT), aspartate aminotranferase (AST), C–Reactive Protein (CRP) and Interleukin-6 (IL–6) were estimated before and after exercise. Serum CK, LDH, AST, ALT, CRP and IL–6 levels significantly increased after exercise in both the groups in comparison to respective pre–exercise values. Although CK, LDH, CRP and IL–6 responses were significantly higher in postpubertal boys, no intergroup variation was noted in post-exercise ALT activity. Age and body mass index (BMI) had significant positive correlation with post-exercise CK, LDH, AST, CRP, and IL–6 levels. Muscle injury and inflammation were significantly higher in postpubertal boys, suggesting a rise in these responses as a function of age and muscle mass during onset of puberty. Post–exercise release pattern of ALT was not influenced by age and puberty. Data also revealed that concentric endurance exercise did not induce extensive muscle damage and inflammation in both the groups. Drastic elevation in IL–6 level despite lower muscle damage implied that this marker was released from contracting muscle fibers independent of muscle damage and acute inflammation. The magnitude of this post–exercise IL–6 release increased as a function of age and BMI.

Acute Effects of Running on Shear Wave Elastography Measures of the Achilles Tendon and Calf Muscles in Professional Female Handball and Volleyball Players.

Shear Wave Elastography (SWE) is currently used to detect tissue pathologies, i.e., tendinopathy. For preventive medicine, it is important to examine the sensitivity of SWE and to investigate how stiffness measures are affected by methodological variables. The aim of this study is to examine shear wave elastography (SWE) measures in order to compare the pre- and post-running values and to determine the correlation between the shear wave speed values (m/s). SWE examinations of the Achilles tendon (AT), soleus muscle (MS) and gastrocnemius muscle (MG)) were performed in 24 healthy professional female athletes. Measurements of the shear wave speed (m/s) were taken before and after incremental treadmill running until exhaustion. Correlations were investigated using the Pearson correlation coefficient and were examined for significance using the Student's t-test. The pre- and post-exercise shear wave speed did not differ. The pre-exercise and post-exercise stiffness for MS (r = 0.613), MG (r = 0.609) and AT (r = 0.583) correlated strongly. The pre-exercise values and changes in stiffness showed a significant correlation (p < 0.001). In professional athletes, acute exercise induces different tissue stiffness changes in AT, MS and MG for each individual. Thus, exercise activity immediately prior to the SWE measurement needs to be factored in when evaluating tissue stiffness.

Physiological Variables that Contribute to Aerobic Fitness in Boys during Early Adolescence in the Context of Basketball Training and the Maturity Level.

The aim of this study was to assess physiological variables that contribute to aerobic fitness in respect to basketball training and the maturity level in adolescent boys. Our subjects were 28 basketball-trained and 22 control-group boys (average age: 11.83 ± 0.43 years). An incremental treadmill running test to exhaustion was performed twice with a 1-year interval between the sessions to determine the following peak aerobic fitness variables: oxygen uptake, stroke volume, cardiac output, minute ventilation, and others. Maturity offset was used to evaluate the maturity level. The basketball-trained group exhibited a higher peak ratio-scaled oxygen uptake (1st session: 50.55 ± 6.21 and 46.57 ± 5.68 ml/kg/min in basketball and control-group boys, respectively, p = 0.024; 2nd session: 54.50 ± 6.50 and 45.33 ± 5.99 ml/kg/min, respectively, p < 0.001) during both testing sessions. During the 2nd session, the basketball-trained group also showed a significantly higher peak arteriovenous oxygen difference (basketball-trained boys: 14.02 ± 2.17 ml/100 ml; control-group boys: 12.52 ± 2.49 ml/100 ml; p = 0.027) and peak minute ventilation (basketball-trained boys: 96.08 ± 21.71 l/min; control-group boys: 83.14 ± 17.85 l/min; p = 0.028). The maturity level among the basketball-trained boys was correlated with peak variables: oxygen uptake, stroke volume, cardiac output, and minute ventilation, but not with the ratio-scaled oxygen uptake. In conclusion, basketball training at a young age among boys improved aerobic fitness compared with sedentary boys. More mature basketball players were not superior to their less mature peers regarding aerobic fitness after adjusting for body dimensions.

The Acute Effects of a Maple Water Drink on Exercise Responses, Oxidative Stress and Inflammation in Overweight College Males

The purpose of this study was to examine the acute effect of maple water on exercise responses and biomarkers of post-exercise inflammation and muscle damage in an overweight male college population. The initial study used a single blind, pre/post exercise design, where the participants (N=10) consumed maple water or placebo (355ml/12 fluid oz) prior to an incremental treadmill running protocol to exhaustion and returned one week later to consume the opposite treatment and repeated the maximal bout of exercise. During each exercise bout, finger-stick measures of blood glucose were taken, along with venipuncture measures for inflammatory markers, oxidative stress and muscle damage. Analysis of the data revealed a significant decrease in 2 anti-inflammatory markers IL-4 (p<0.001) and IL-10 (p=0.026), a significant decrease in 1 pro-inflammatory marker IL-12 (p=0.022), and a significant increase in oxygen consumption during exercise (p=0.045). Early outcomes indicate maple water has positive benefits for those that exercise in the areas of cardiovascular fitness and post exercise inflammation.

Reliability of physical performance and thermoregulatory parameters in rats subjected to incremental treadmill running

Thermoregulatory changes may influence the rats' prolonged physical performance and are commonly evaluated during treadmill running. Therefore, we determined the reliability of performance and thermoregulatory parameters in rats subjected to incremental-speed exercises (i.e., we assessed whether the testing protocol provides measurements that are consistent and free from error). Twenty rats were subjected to two sessions of incremental exercises at 24 °C, separated by 48 h, until they were fatigued. The rats' performance and thermoregulatory responses were determined, and values concerning the reliability of these parameters [e.g., intraclass correlation coefficient (ICC) and minimal detectable change (MDC)] were calculated. Our data revealed that the core temperature (TCORE) at fatigue and heat loss threshold were the most reproducible parameters, showing good reliability (ICC between 0.75 and 0.90). Moreover, all performance parameters assessed, the change in TCORE, the rate of TCORE increase, and the TCORE increase-to-distance traveled ratio presented moderate reliability. We then investigated whether changes in performance and thermoregulation induced by a warm environment were greater than the MDC95% values determined in the first experiment. Eight rats were subjected to incremental exercises at two environmental conditions: 24 °C and 31 °C. Individual analyses showed that most rats presented thermoregulatory differences between exercises at 31 °C and 24 °C greater than the calculated MDC95% values; this was not the case for their performance. In conclusion, we provide data on the reliability of rats’ performance and thermoregulatory parameters during incremental-speed running. Also, the exercise in a warm environment produced detectable thermoregulatory changes relative to the exercise under temperate conditions.

Store-Operated Ca2+ Entry in Skeletal Muscle Contributes to the Increase in Body Temperature during Exertional Stress.

Exertional heat stroke (HS) is a hyperthermic crisis triggered by an excessive accumulation of Ca2+ in skeletal muscle fibers. We demonstrated that exercise leads to the formation of calcium entry units (CEUs), which are intracellular junctions that reduce muscle fatigue by promoting the recovery of extracellular Ca2+ via store-operated Ca2+ entry (SOCE). Here, we tested the hypothesis that exercise-induced assembly of CEUs may increase the risk of HS when physical activity is performed in adverse environmental conditions (high temperature and humidity). Adult mice were: (a) first, divided into three experimental groups: control, trained-1 month (voluntary running in wheel cages), and acutely exercised-1 h (incremental treadmill run); and (b) then subjected to an exertional stress (ES) protocol, a treadmill run in an environmental chamber at 34 °C and 40% humidity. The internal temperature of the mice at the end of the ES was higher in both pre-exercised groups. During an ES ex-vivo protocol, extensor digitorum longus(EDL) muscles from the trained-1 month and exercised-1 h mice generated greater basal tension than in the control and were those that contained a greater number of CEUs, assessed by electron microscopy. The data collected suggest that the entry of Ca2+ from extracellular space via CEUs could contribute to exertional HS when exercise is performed in adverse environmental conditions.

Differences between Elite Male and Female Badminton Athletes Regarding Heart Rate Variability, Arterial Stiffness, and Aerobic Capacity.

Cardiovascular health and aerobic capacity play crucial roles in determining the performance of athletes in the highly competitive sport of badminton. Few studies have directly compared heart rate variability (HRV), arterial stiffness, and aerobic capacity between male and female athletes, especially among badminton athletes. This study investigated sex differences in HRV, arterial stiffness, and aerobic capacity in badminton athletes. Elite badminton athletes were recruited and divided into male (n = 20, 21.0 ± 1.8 years old) and female (n = 16, 21.2 ± 2.3 years old) groups. Both groups performed an incremental treadmill running test for the evaluation of maximal oxygen consumption (O2max), anaerobic threshold, and time to exhaustion. They started exercising at a treadmill speed of 2.7 km/h and an inclination of 10% gradient for 3 min, and the speed and inclination were gradually increased every 3 min until they were exhausted or fatigued volitionally. HRV was examined using the Polar heart rate monitor over a period of 5 min at rest in the supine position. Subsequently, the index of arterial stiffness was examined under the same condition. Our results revealed significant differences between the male and female athletes in O2max (men: 60.38 ± 8.98 mL/kg/min, women: 48.13 ± 7.72 mL/kg/min, p < 0.05), anaerobic threshold (men: 41.50 ± 7.26 mL/kg/min, women: 32.51 ± 6.19 mL/kg/min, p < 0.05), time to exhaustion (men: 902.15 ± 120.15 s, women: 780.56 ± 67.63 s, p < 0.05), systolic blood pressure (men: 125.27 ± 7.76 mmHg, women: 107.16 ± 11.09 mmHg, p < 0.05), and arterial stiffness index (men: 63.56 ± 12.55, women: 53.83 ± 8.03, p < 0.05). However, no significant differences in HRV measures were observed between the two groups. These findings suggested that the male badminton athletes demonstrated significantly higher aerobic capacity than did the female athletes, but there were no significant differences in HRV measures. The female athletes exhibited superior arterial function, compared with their male counterparts.

Comparison of the Cardiovascular Effects of Extreme Psychological and Physical Stress Tests in Male Soccer Players.

Background: The purpose of our study was to compare the physiological effects of extreme physical and psychological stress tests in male soccer players, since these two types of stress apply to athletes with high performance requirements. Methods: A total of 63 healthy male soccer players participated in this study, all of whom underwent both of the tests. A physical stress test was carried out in an exercise physiology laboratory, where subjects completed an incremental treadmill running test to full exhaustion, and a psychological test was performed in a military tactical room, where subjects met a street offence situation. Heart rate variability (HRV) and blood pressure (BP) were recorded directly before, immediately after, and 30 min after the stress tests. Results: The majority of HRV indices changed significantly in both stress protocols. Inverse, significant changes (positive for the physical test, negative for the psychological test, p < 0.001) were found when comparing the alterations of HRV indices between the tests. Significant differences were found in the changes in systolic (p = 0.003) and diastolic (p < 0.001) BP between the test protocols, and also between the baseline and post-test measurements (p < 0.001). Conclusion: Both HRV and BP are sensitive physiological parameters to measure the impact of extreme physical and/or psychological stress

Exercise-activated Ca2+ entry and enhanced risk of heat stroke

Exertional/environmental heat strokes (EHSs) are hyperthermic crises triggered by strenuous physical exercise and/or exposure to environmental heat, and are caused by an altered intracellular Ca2+ homeostasis in muscle. We recently demonstrated that a single bout of exercise on treadmill leads to formation of calcium entry units (CEUs), intracellular junctions that promote interaction between STIM1 and Orai1, the two proteins that mediate store-operated Ca2+ entry (SOCE). SOCE is a mechanism that is activated during muscle fatigue and that allows for recovery of extracellular Ca2+ during prolonged activity. The hypothesis underlying this work is that assembly of CEUs during prolonged exercise may predispose to EHSs when exercise is performed in challenging environmental conditions. To test this hypothesis, 4-mo-old mice were (1) divided into three experimental groups: control, trained-1m (1 mo of voluntary running in wheel cages), and exercised-1h (1 h of incremental treadmill run); and (2) subjected to an exertional stress (ES) protocol consisting of an incremental 45-min treadmill run at 34°C and 40% humidity. We then (a) measured the internal temperature of mice, which was higher in the two pre-exercised groups (trained-1m: 38.9°C ± 0.33; exercised-1h: 38.7°C ± 0.40) compared with control animals (37.9°C ± 0.17); (b) applied an ex vivo ES protocol to isolated EDL muscles (tetanic stimulation performed at 30°C) and verified that samples from trained-1m and exercised-1h mice generated a tension significantly greater than control samples; and (c) analyzed CEUs by electron microscopy (EM) and verified that EDL muscles of trained-1m and exercised-1h mice contained a greater number of membranes elements forming CEUs. The data collected indicates that the presence of CEUs correlates with a greater increase in body temperature and could, in principle, predispose to EHS when exercise is performed in challenging environmental conditions.

Correlation of maximal respiratory exchange ratio with anaerobic power and maximal oxygen uptake in anaerobic trained athletes

Background and Study Aim. The respiratory exchange ratio (RER) is the ratio of the amount of carbon dioxide produced (VCO2) to the amount of oxygen uptake (VO2) is important. It indirectly informs about the predominant metabolic pathway to provide the energy needed during exercise. The relationship of maximal RER with aerobic and anaerobic capacity in athletes remains unclear. The purpose of this study was to investigate the relationship between maximal RER and anaerobic power and maximal oxygen uptake (VO2max) in anaerobic trained athletes.&#x0D; Material and Methods. Thirteen male alpine skiers (age 18.1 ± 3.1 years) competing in national and international competitions participated in the study. Athletes first performed an incremental treadmill run test to determine their VO2max (ml/kg/min), maximal RER (VCO2 / VO2) and maximal running speed (km/h). After 48 hours, the athletes performed the Wingate anaerobic test to determine peak power, mean power, minimum power, and fatigue index. Pearson correlation coefficients were used to examine the relations between variables.&#x0D; Results. Maximal RER was positively correlated with peak power (r = 0.587, p &lt; 0.035), mean power (r = 0.656, p &lt; 0.015) and minimum power (r = 0.674, p &lt; 0.012). Maximal RER did not significantly correlate with fatigue index (p &gt; 0.05). Maximal RER was negatively correlated with the VO2max (r = – 0.705, p &lt; 0.007) and maximal running speed (r = – 0.687, p &lt; 0.01).&#x0D; Conclusions. Maximal RER may be useful for evaluating anaerobic capacity in anaerobic-trained athletes. Measuring the maximal RER values of athletes during incremental exercise may provide information about physiological adaptations in response to physical training.

Sensitivity of movement features to fatigue during an exhaustive treadmill run

ABSTRACT The objective of the present study was to examine the sensitivity of several movement variables during running to exhaustion adopting a cross-sectional design. Thirteen recreational runners, that systematically trained and competed, performed an exhaustive running protocol on an instrumented treadmill. Respiratory data were collected to establish the ventilatory threshold in order to obtain a reference point regarding the gradual accumulation of fatigue. A machine learning approach was adopted to analyse a set of 29,650 data points (individual steps) of kinetic and kinematic data, using a random forest classifier for the region pre and post the ventilatory threshold. The overall accuracy of the model was 0.914 (95% CI: 0.907–0.919). The four most important variables, and more sensitive in predictive ability, as it was concluded from the variable importance procedure and the partial dependence (PD), were the angular range in AP axis of upper trunk C7, the maximum loading rate, the angular range in LT axis of the C7 and the maximum value of the ground reaction force. Two-dimensional PD revealed considerable interactions for certain areas of the joint distributions between kinetic and kinematic data. These results provide a direction towards understanding the interconnections of kinetics and kinematics of the torso to maintain the coordinated running pattern under fatigue conditions. Highlights Trunk frontal plane kinematics is the most sensitive parameter to fatigue. Practitioners should consider this finding during endurance training. Kinetics exhibit a stable linear increase in mean values but a non-linear increase in variance during an exhaustive incremental treadmill run. This may affect training at a submaximal fatigued state. Specific areas in the joint distributions of kinetics and kinematics during treadmill running exhibit increased sensitivity in predicting fatigue state.

Detection of the Anaerobic Threshold in Endurance Sports: Validation of a New Method Using Correlation Properties of Heart Rate Variability.

Past attempts to define an anaerobic threshold (AnT) have relied upon gas exchange kinetics, lactate testing and field-based evaluations. DFA a1, an index of heart rate (HR) variability (HRV) fractal correlation properties, has been shown to decrease with exercise intensity. The intent of this study is to investigate whether the AnT derived from gas exchange is associated with the transition from a correlated to uncorrelated random HRV pattern signified by a DFA a1 value of 0.5. HRV and gas exchange data were obtained from 15 participants during an incremental treadmill run. Comparison of the HR reached at the second ventilatory threshold (VT2) was made to the HR reached at a DFA a1 value of 0.5 (HRVT2). Based on Bland–Altman analysis and linear regression, there was strong agreement between VT2 and HRVT2 measured by HR (r = 0.78, p < 0.001). Mean VT2 was reached at a HR of 174 (±12) bpm compared to mean HRVT2 at a HR of 171 (±16) bpm. In summary, the HR associated with a DFA a1 value of 0.5 on an incremental treadmill ramp was closely related to that of the HR at the VT2 derived from gas exchange analysis. A distinct numerical value of DFA a1 representing an uncorrelated, random interbeat pattern appears to be associated with the VT2 and shows potential as a noninvasive marker for training intensity distribution and performance status.

Effects of Velocity Loss Threshold Within Resistance Training During Concurrent Training on Endurance and Strength Performance.

This study analyzed the effects of 3 training interventions: 1 isolated endurance training (ET) and 2 concurrent training (CT), which differed in the velocity loss (VL) magnitude allowed during the resistance training (RT) set: 15% (VL15) versus 45%, on strength and endurance running performance. A total of 33 resistance- and endurance-trained men were randomly allocated into 3 groups: VL15, VL 45%, and ET. ET was similar across all groups. The CT groups differed in the VL allowed during the RT set. Before and after the 8-week training program the following tests were performed: (1) running sprints, (2) vertical jump, (3) progressive loading test in the squat exercise, and (4) incremental treadmill running test up to maximal oxygen uptake. Significant differences (P < .001) in RT volume (approximately 401 vs 177 total repetitions for VL 45% and VL15, respectively) were observed. Significant "group" × "time" interactions were observed for vertical jump and all strength-related variables: the CT groups attained significantly greater gains than ET. Moreover, a significant "group" × "time" interaction (P = .03) was noted for velocity at maximal oxygen uptake. Although all groups showed increases in velocity at maximal oxygen uptake, the VL15 group achieved greater gains than the ET group. CT interventions experienced greater strength gains than the ET group. Although all groups improved their endurance performance, the VL15 intervention resulted in greater gains than the ET approach. Therefore, moderate VL thresholds in RT performed during CT could be a good strategy for concurrently maximizing strength and endurance development.

Blood lactate kinetics during incremental treadmill vs. prolonged field running in crosscountry skiers

Blood lactate kinetics during incremental treadmill vs. prolonged field running in crosscountry skiers

Physical performance level in sarcomeric mitochondria creatine kinase knockout mouse model throughout ageing.

The objective of the present study was to establish the role of sarcomeric mitochondrial creatine kinase (Mt-CK) in muscle energy output during exercise in a murine model of ageing (the Mt-CK knock-out mouse, Mt-CK-/-). Three age groups of Mt-CK-/- mice and control male mice (6, 9, and 18months of age) underwent incremental treadmill running tests. The maximum speed (Vpeak) and maximal oxygen consumption (VO2peak) values were recorded. Urine samples were analyzed using metabolomic techniques. The skeletal muscle (quadriceps) expression of proteins involved in mitochondria biogenesis, peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) and dynamin-related GTPase mitofusin 2 (Mnf2) were quantified. The VO2 peak (normalized to heart weight: HW) of 18-month-old (mo) Mt-CK-/- mice was 27% (p<0.001) lower than in 18-mo control mice. The VO2peak/HW ratio was 29% (p<0.001) lower in 18-mo Mt-CK-/- mice than in 6-mo (p<0.001) and 32% (p<0.001) than 9-mo Mt-CK-/- mice. With a 0° slope, Vpeak was 10% (p<0.05) lower in 18-mo Mt-CK-/- mice than in 6-mo Mt-CK-/- mice but did not differ when comparing the 18-mo and 6-mo control groups. The skeletal muscles weight normalized on body weight in 6-mo Mt-CK-/- were 13 to 14% (p<0.001, p<0.05) lower versus the 6-mo control, in addition, the presence of branched-chain amino acids in the urine of 6-mo Mt-CK-/- mice suggests an imbalance in protein turnover (catabolism rather than anabolism) but we did not observe any age-related differences. The expression of PGC-1α and Mnf2 proteins in the quadriceps showed that age-related effects were more prominent than genotype effects. The present study showed ageing is potentialized by Mt-CK deficiency with regard to VO2peak, Vpeak and mitochondrial protein expression. Our results support that Mt-CK-/- mice undergo physiological adaptations, enabling them to survive and to perform as well as wild-type mice. Furthermore, it is possible that these adaptations in Mt-CK-/- mice have a high energy cost and might trigger premature ageing.

Influence of Artefact Correction and Recording Device Type on the Practical Application of a Non-Linear Heart Rate Variability Biomarker for Aerobic Threshold Determination.

Recent study points to the value of a non-linear heart rate variability (HRV) biomarker using detrended fluctuation analysis (DFA a1) for aerobic threshold determination (HRVT). Significance of recording artefact, correction methods and device bias on DFA a1 during exercise and HRVT is unclear. Gas exchange and HRV data were obtained from 17 participants during an incremental treadmill run using both ECG and Polar H7 as recording devices. First, artefacts were randomly placed in the ECG time series to equal 1, 3 and 6% missed beats with correction by Kubios software’s automatic and medium threshold method. Based on linear regression, Bland Altman analysis and Wilcoxon paired testing, there was bias present with increasing artefact quantity. Regardless of artefact correction method, 1 to 3% missed beat artefact introduced small but discernible bias in raw DFA a1 measurements. At 6% artefact using medium correction, proportional bias was found (maximum 19%). Despite this bias, the mean HRVT determination was within 1 bpm across all artefact levels and correction modalities. Second, the HRVT ascertained from synchronous ECG vs. Polar H7 recordings did show an average bias of minus 4 bpm. Polar H7 results suggest that device related bias is possible but in the reverse direction as artefact related bias.

A New Detection Method Defining the Aerobic Threshold for Endurance Exercise and Training Prescription Based on Fractal Correlation Properties of Heart Rate Variability.

The short-term scaling exponent alpha1 of detrended fluctuation analysis (DFA a1), a nonlinear index of heart rate variability (HRV) based on fractal correlation properties, has been shown to steadily change with increasing exercise intensity. To date, no study has specifically examined using the behavior of this index as a method for defining a low intensity exercise zone. The aim of this report is to compare both oxygen intake (VO2) and heart rate (HR) reached at the first ventilatory threshold (VT1), a well-established delimiter of low intensity exercise, to those derived from a predefined DFA a1 transitional value. Gas exchange and HRV data were obtained from 15 participants during an incremental treadmill run. Comparison of both VO2 and HR reached at VT1 defined by gas exchange (VT1 GAS) was made to those parameters derived from analysis of DFA a1 reaching a value of 0.75 (HRVT). Based on Bland Altman analysis, linear regression, intraclass correlation (ICC) and t testing, there was strong agreement between VT1 GAS and HRVT as measured by both HR and VO2. Mean VT1 GAS was reached at 39.8 ml/kg/min with a HR of 152 bpm compared to mean HRVT which was reached at 40.1 ml/kg/min with a HR of 154 bpm. Strong linear relationships were seen between test modalities, with Pearson’s r values of 0.99 (p < 0.001) and.97 (p < 0.001) for VO2 and HR comparisons, respectively. Intraclass correlation between VT1 GAS and HRVT was 0.99 for VO2 and 0.96 for HR. In addition, comparison of VT1 GAS and HRVT showed no differences by t testing, also supporting the method validity. In conclusion, it appears that reaching a DFA a1 value of 0.75 on an incremental treadmill test is closely associated with crossing the first ventilatory threshold. As training intensity below the first ventilatory threshold is felt to have great importance for endurance sport, utilization of DFA a1 activity may provide guidance for a valid low training zone.