Effects of strength training on repeated sprint ability in team sports players: a systematic review.

Objective: This systematic review was conducted to analyze the existing evidence on the effects of strength training (ST) and complex/contrast training (CCT) on repeated sprint ability (RSA) in team sports players. Methods: A systematic review of the literature was performed following the PRISMA statement. PubMed, Web of Science, and Scopus databases were used. Original full-text articles were analyzed, without date restriction until May 26, 2024, written in English, peer-reviewed, and for eligibility must have included (1) male or female team sports players, amateur or professional category, without age restriction (2) lower extremity ST and/or CCT program (3) active control group (4) running RSA test (e.g., repeated shuttle sprint ability test or straight-line repeated sprint ability test) before and after the intervention period (5) controlled trial. Results: A total of 3,376 studies were identified and screened. Finally, 10 articles were included based on the inclusion and exclusion criteria, all with moderate methodological quality according to the PEDro scale. The best time, mean time, and total time presented significant pre and post-test changes, using ST in 3, 2, and 1 experimental groups, respectively, and using CCT in 1, 1, and 1 experimental groups, respectively, with almost no differences in the percentage decrement most commonly reported in RSA tests. There were no changes in the control groups. Conclusion: Together, ST performed in a range of maximal power provides benefits in the best time and mean time and performed between 80 to 95% of 1 repetition maximum (RM) provides benefits in the best time, mean time, and total time in RSA tests. CCT performed between 75 to 90% of 1 RM combined with jumps and sprints provides benefits in the best time, mean time, and total time in RSA test, but no unaltered percentage decrement in ST and CCT in elite and semi-professional team sport players.

Agreement of ultra-short-term heart rate variability measure after different repeated bouts of sprint ability tests.

This study aims to explore: (1) the validity of post-exercise ultra-short-term heart rate variability (HRVust) after two different bouts of repeated sprint ability test (RSA), and (2) the relationship between HRVust measure and RSA performance. Twenty adolescent male futsal players voluntarily participated in this study (age: 17.65 ± 1.81 years, body height: 170.88 ± 4.98 cm, body weight: 61.78 ± 4.67 kg). The participants performed a standard RSA test (RSAstandard) and an RSA test with a 10% decrement of the best sprint time test (RSA10%decrement) on two separate occasions within a week. On both occasions, a 5-min resting electrocardiography was administered pre- and post-RSA exercise protocols. The first 30-s (HRVust30s), 60-s (HRVust60s), and 60-120-s (HRVust1-2min) were extracted and used to compare with the standard of 5-min HRV recording (HRVcriterion). The natural logarithm (ln) of the standard deviation of normal-to-normal intervals (SDNN) and root mean square of successive normal-to-normal interval differences (RMSSD) HRV indices were utilised to establish intraclass correlation coefficient (ICC2,1), coefficient of variation (%CV), and Pearson product-moment correlation (r). Results revealed the ICC values of HRVust lnSDNN (RSAstandard = 0.77-0.88; RSA10%decrement = 0.41-0.71) and lnRMSSD (RSAstandard = 0.81-0.86; RSA10%decrement = 0.57-0.82). Furthermore, significantly positive correlations between best sprint time and post-exercise HRVust indices were found in lnSDNN (r = 0.47-0.62; p < 0.05) and lnRMSSD (r = 0.45; p < 0.05). Additionally, a large CV of lnSDNN (RSAstandard = 32%-45%; RSA10%decrement = 29%-39%), lnRMSSD (RSAstandard = 50%-66%; RSA10%decrement = 48%-52%), and ratio (RSAstandard = 45%-126%; RSA10%decrement = 27%-45%) was found after the RSA protocols. In conclusion, the number of bouts of RSA exercise potentially influences the agreement of post-exercise time-domain HRVust indices to standard HRV measure.

Mechanical Deviations in Stride Characteristics During Running in the Severe Intensity Domain Are Associated With a Decline in Muscle Oxygenation.

We explored the impact of running in the severe intensity domain on running mechanics and muscle oxygenation in competitive runners by investigating the relationship between mechanical deviations from typical stride characteristics and muscle oxygen saturation (SmO2) in the quadriceps muscle. Sixteen youth competitive runners performed an 8-min exhaustive running test on an outdoor track. Running mechanics were continuously monitored using inertial measurement units. Rectus femoris SmO2 and total hemoglobin (a measure of blood volume) were continuously monitored by near-infrared spectroscopy. One-class support vector machine (OCSVM) modeling was employed for subject-specific analysis of the kinematic data. Statistical analysis included principal component analysis, ANOVA, and correlation analysis. Mechanical deviations from typical stride characteristics increased as the running test progressed. Specifically, the percentage of outliers in the OCSVM model rose gradually from 2.2 ± 0.8% at the start to 43.6 ± 28.2% at the end (p < 0.001, mean ± SD throughout). SmO2 dropped from 74.3 ± 8.4% at baseline to 10.1 ± 6.8% at the end (p < 0.001). A moderate negative correlation (r = -0.61, p = 0.013) was found between the average SmO2 and the percentage of outlier strides during the last 15% of the run. During high-intensity running, alterations in running biomechanics may occur, linked to decreased quadriceps muscle oxygenation. These parameters highlight the potential of using running kinematics and muscle oxygenation in training to optimize performance and reduce injury risks. Our research contributes to understanding biomechanical and physiological responses to endurance running and emphasizes the importance of individualized monitoring.

Effects of shoe heel height on ankle dynamics in running.

Shoes affect the evolved biomechanics of the foot, potentially affecting running kinematics and kinetics that can in turn influence injury and performance. An important feature of conventional running shoes is heel height, whose effects on foot and ankle biomechanics remain understudied. Here, we investigate the effects of 6-26 mm increases in heel height on ankle dynamics in 8 rearfoot strike runners who ran barefoot and in minimal shoes with added heels. We predicted higher heels would lead to greater frontal plane ankle torques due to the increased vertical moment arm of the mediolateral ground reaction force. Surprisingly, the torque increased in minimal shoes with no heel elevation, but then decreased with further increases in heel height due to changes in foot posture. We also found that increasing heel height caused a large increase in the ankle plantarflexion velocity at heel strike, which we explain using a passive collision model. Our results highlight how running in minimal shoes may be significantly different from barefoot running due to complex interactions between proprioception and biomechanics that also permit runners to compensate for modifications to shoe design, more in the frontal than sagittal planes.

[Study on novel inflammatory indicators in marathon exercise monitoring].

To analyze the changes in lactate dehydrogenase, creatine kinase, creatine kinase isoenzyme, high-sensitivity troponin T, N-terminal B-type natriuretic peptide precursor, homocysteine, and novel inflammatory indices (neutrophil-lymphocyte ratio, platelet-lymphocyte ratio, systemic immune-inflammation index) before and after competitions in amateur marathon runners, and to assess the effects of myocardial injury due to acute exercise and the value of novel inflammatory indices in marathon exercise monitoring. This paper is an analytical study. Amateur athletes recruited by Beijing Hospital to participate in the 2022 Beijing Marathon and the 2023 Tianjin Marathon, and those who underwent health checkups at the Beijing Hospital Medical Checkup Center from January to June 2023 were selected as the study subjects, and 65 amateur marathon runners (41 males and 24 females) and 130 healthy controls (82 males and 48 females) were enrolled in the study according to the inclusion criteria. Peripheral blood was collected one week before, immediately after, and one week after running, and routine blood tests, cardiac enzymes, infarction markers, N-terminal B-type natriuretic peptide precursor, and homocysteine were performed to calculate the values of novel inflammatory indexes. Wilcoxon signed-rank test and Spearman's rank correlation analysis were used to compare the differences in the levels of each index between the amateur marathon population and the health checkup population, and to compare the changes and correlations of each index at the three time points in the amateur marathoners.The results showed that the neutrophil-lymphocyte ratios of the healthy physical examination population and 65 amateur marathoners 1 week before running were 1.73 (1.33, 2.16) and 1.67 (1.21, 2.16), the platelet-lymphocyte ratios were 122.75 (96.69, 155.89) and 120.86 (100.74, 154.63), and the systemic immune inflammation index was 398.62 (274.50, 538.69) and 338.41 (258.62, 485.38), etc.; on 1 week before running, immediately after running and 1 week after running, lactate dehydrogenase of 65 amateur marathon runners was 173.00(159.00, 196.50)U/L,284.00(237.50, 310.50)U/L, 183.00(165.50, 206.50)U/L, creatine kinase was 131.00(94.30, 188.20)U/L,318.00(212.00, 573.15)U/L,139.00(90.55, 202.40)U/L, creatine kinase isoenzyme was 2.50(1.76, 3.43)µg/L,6.24(4.87, 10.30)µg/L,2.73(1.57, 4.40)µg/L.In 65 amateur marathon runners, lactate dehydrogenase, creatine kinase, creatine kinase isoenzyme, high sensitivity troponin T, N-terminal B-type natriuretic peptide precursor, homocysteine, and novel inflammation markers were significantly elevated in the immediate post-run period compared with 1 week before the run, and the differences were statistically significant (Z=-7.009, Z=-6.813, Z=-6.885, Z=-7.009, Z=-7.009, Z=-6.656; P<0.05 for the above indicators).Neutrophil-lymphocyte ratio, platelet-lymphocyte ratio, and systemic immune-inflammatory index all showed significant positive correlation with the pre-and post-run rates of change of high-sensitivity troponin T (ρ=0.28, P=0.03;ρ=0.31, P=0.01;ρ=0.27, P=0.03); these 3 markers were also significantly and positively correlated with the pre-and post-run rates of change in a collection of myocardial-related markers such as lactate dehydrogenase, creatine kinase, creatine kinase isozymes, high-sensitivity troponin T, N-terminal B-type natriuretic peptide precursor, and homocysteine, respectively(r=0.446, P=0.039; r=0.452, P=0.033; r=0.449, P=0.036).In addition, the platelet-lymphocyte ratio was positively correlated with the pre-and post-run rates of change in creatine kinase and creatine kinase isoenzymes(ρ=0.27, P=0.03;ρ=0.28, P=0.02).In conclusion, acute myocardial injury may be triggered during marathon exercise. Changes in novel inflammatory markers were significantly associated with changes in myocardial enzymes, infarction markers, N-terminal B-type natriuretic peptide precursors, and homocysteine, which may be of value for the prediction of myocardial injury during exercise.

Hamstrings on focus: Are 72 hours sufficient for recovery after a football (soccer) match? A multidisciplinary approach based on hamstring injury risk factors and histology.

This study aimed to assess acute and residual changes in sprint-related hamstring injury (HSI) risk factors after a football (soccer) match, focusing on recovery within the commonly observed 72-h timeframe between elite football matches. We used a multifactorial approach within a football context, incorporating optical and ultrastructural microscopic analysis of BFlh (biceps femoris long head) muscle fibres, along with an examination of BFlh fibre composition. Changes in sprint performance-related factors and HSI modifiable risk factors were examined until 3 days after the match (MD +3) in 20 football players. BFlh biopsy specimens were obtained before and at MD +3 in 10 players. The findings indicated that at MD +3, sprint-related performance and HSI risk factors had not fully recovered, with notable increases in localized BFlh fibre disruptions. Interestingly, match load (both external and internal) did not correlate with changes in sprint performance or HSI risk factors nor with BFlh fibre disruption. Furthermore, our study revealed a balanced distribution of ATPase-based fibre types in BFlh, with type-II fibres associated with sprint performance. Overall, the results suggest that a 72-h recovery period may not be adequate for hamstring muscles in terms of both HSI risk factors and BFlh fibre structure following a football match.

High-Intensity GPS-Derived Parameters in Semi-Professional Soccer: Home vs. Away Roles of the Team and Their Relationship with the Match's Final Score.

High-intensity activities are related to success in football. We looked at whether high-intensity activity differed between home and away matches and its impact on the final score. Thirty football players (20.3 ± 0.8 years) were recruited from a Spanish semi-professional team. Footballers wore a GPS device to monitor high-intensity parameters from competition matches. The final score of every match was also recorded. Playing at home showed greater total distance (TD) > 24 km/h, >27 km/h, >85% Vmax, and the number of sprints > 24 km/h (all p < 0.05) than playing away. Positive correlations were also found between the match score and high-speed running (HSR) distance covered by the team per minute (r = 0.401), TD > 21 km/h (r = 0.417), TD > 24 km/h (r = 0.343), number of sprints > 24 km/h (r = 0.337), and HSR per minute (r = 0.459) (all p < 0.05). The results suggest that playing at home is associated with greater high-intensity effort than playing away. Moreover, the volume of high-intensity effort influences the final score.

Center of Pressure Measurement Accuracy via Insoles with a Reduced Pressure Sensor Number during Gaits.

The objective was to compare simplified pressure insoles integrating different sensor numbers and to identify a promising range of sensor numbers for accurate center of pressure (CoP) measurement. Twelve participants wore a 99-sensor Pedar-X insole (100 Hz) during walking, jogging, and running. Eight simplified layouts were simulated, integrating 3-17 sensors. Concordance correlation coefficients (CCC) and root mean square errors (RMSE) between the original and simplified layouts were calculated for time-series mediolateral (ML) and anteroposterior (AP) CoP. Differences between layouts and between gait types were assessed via ANOVA and Friedman test. Concordance between the original and simplified layouts varied across layouts and gaits (CCC: 0.43-0.98; χ(7)2 ≥ 34.94, p < 0.001). RMSEML and RMSEAP [mm], respectively, were smaller in jogging (5 ± 2, 15 ± 9) than in walking (8 ± 2, 22 ± 4) and running (7 ± 4, 20 ± 7) (ηp2: 0.70-0.83, p < 0.05). Only layouts with 11+ sensors achieved CCC ≥ 0.80 in all tests across gaits. The 13-sensor layout achieved CCC ≥ 0.95 with 95% confidence, representing the most promising compromise between sensor number and CoP accuracy. Future research may refine sensor placement, suggesting the use of 11-13 sensors. For coaches, therapists, and applied sports scientists, caution is recommended when using insoles with nine or fewer sensors. Consulting task-specific validation results for the intended products is advisable.

Combined Impact of Creatine, Caffeine, and Variable Resistance on Repeated Sprint Ability in Young Soccer Players.

There is evidence that both intra-serial variable resistance (I-sVR), as pre-activation within the post-activation performance enhancement cycle (PAPE), and creatine and caffeine supplementation increase athletic performance in isolation. However, the effect of the three conditioning factors on 30 m repeated sprint ability (RSA) performance in young soccer players is unknown. This study determined the summative and isolation effect of ergogenic aids and pre-activation in half-back squats (HBSs) with I-sVR on performance in an RSA test in young soccer players. Twenty-eight young soccer players were randomly assigned to either EG1 (n = 7, creatine + caffeine + I-sVR), EG2 (n = 7, creatine + placebo2 + I-sVR), EG3 (n = 7, placebo1 + caffeine + I-sVR), or EG4 (n = 7, placebo1 + placebo2 + I-sVR), using a factorial, four-group-matched, double-blind, placebo-controlled design. Creatine supplementation included 0.3 g/kg/day for 14 days, caffeine supplementation included 0.3 mg/kg per day, and pre-activation in HBS with I-sVR (1 × 5 at 30% 1RM [1.0-1.1 m/s] + 1 × 4 at 60% 1RM [0.6-0.7 m/s]). The RSA test and HBS outcomes were evaluated. Three-way ANOVA showed non-significant differences for the RSA test and HBS outcomes (p > 0.05). At the end of this study, it was found that the three ergogenic aids, together, do not generate a summative effect on the physical performance of young soccer players. However, it is important to analyze individual responses to these specific protocols.

Effect of Single High-Dose Vitamin D3 Supplementation on Post-Ultra Mountain Running Heart Damage and Iron Metabolism Changes: A Double-Blind Randomized Controlled Trial.

Exercise-induced inflammation can influence iron metabolism. Conversely, the effects of vitamin D3, which possesses anti-inflammatory properties, on ultramarathon-induced heart damage and changes in iron metabolism have not been investigated. Thirty-five healthy long-distance semi-amateur runners were divided into two groups: one group received 150,000 IU of vitamin D3 24 h prior to a race (n = 16), while the other group received a placebo (n = 19). Serum iron, hepcidin (HPC), ferritin (FER), erythroferrone (ERFE), erythropoietin (EPO), neopterin (NPT), and cardiac troponin T (cTnT) levels were assessed. A considerable effect of ultramarathon running on all examined biochemical markers was observed, with a significant rise in serum levels of ERFE, EPO, HPC, NPT, and cTnT detected immediately post-race, irrespective of the group factor. Vitamin D3 supplementation showed a notable interaction with the UM, specifically in EPO and cTnT, with no other additional changes in the other analysed markers. In addition to the correlation between baseline FER and post-run ERFE, HPC was modified by vitamin D. The ultramarathon significantly influenced the EPO/ERFE/HPC axis; however, a single substantial dose of vitamin D3 had an effect only on EPO, which was associated with the lower heart damage marker cTnT after the run.

Heat stress and the velocity-duration relationship in amateur runners.

Tolerance to high-intensity constant power exercise can be characterized by the hyperbolic power-duration (or velocity-duration) relationship. The hyperbola is defined by the asymptote (critical power or velocity) and the curvature constant (W' or D'). The effects of thermoregulatory stress on middle-distance running performance are equivocal-possibly due to the complexities of the hyperbolic velocity-duration relationship for these relatively short duration events. We aimed to measure the effects of heat stress on the velocity-duration relationship in amateur runners. Fifteen participants (23 ± 6 years) completed a series of constant-velocity running bouts to intolerance in three heat indices (MILD: 20°C, VERY HOT: 38°C, EXTREME: 55°C). Critical velocity (CV) in MILD (3.52 ± 0.86 m/s) was higher than VERY HOT (3.39 ± 0.82 m/s) and EXTREME (3.29 ± 1.05 m/s; F[2.28] = 3.80, p < 0.035) with no effect of thermal stress on D' (F[2.28] = 2.48, p = 0.11). In amateur competitive/recreational runners, heat stress of ≥38°C heat index negatively affected CV. Thus, even during relatively short events, such as middle-distance running where fluid loss is not a primary concern, heat stress may negatively impact performance.

Health-improving effect of running for students of technical specialties.

OBJECTIVE: Aim: To study the dynamics of indicators of the functional state and health of technical specialties students during their long-term running engagement. PATIENTS AND METHODS: Materials and Methods: The research involved 112 students (59 men and 53 women) aged 17-20 years. Two groups of students were formed: group 1 included students who, in addition to compulsory academic physical education training sessions, were not engaged in any type of motor activity on their own; group 2 included students who independently were engaged in recreational running 3 times a week in extracurricular time. RESULTS: Results: It was found that during the research period, both male and female students who were independently engaged in recreational running in extracurricular time showed a significant improvement of such indicators as resting heart rate, vital capacity of the lungs, duration of breath holding during inhalation and exhalation, duration of heart rate recovery after standard exercise, level of endurance development, level of physical health. CONCLUSION: Conclusions: The positive influence of independent running with moderate intensity on the functional state and health of students of technical specialties has been proved. The low efficiency of the physical education system in Ukraine and, accordingly, the insufficient level of motor activity, indicators of functional status, and health of students who, in addition to academic physical education training sessions, did not exercise on their own, were also confirmed.

Higher risk of upper respiratory tract infection post marathon running: when physical exercise becomes a threat to the immune system.

Background: Several studies have reported that marathon runners have a higher risk of upper respiratory tract infections (URTI) post marathon than non-exercising controls. However, other studies did not find a higher risk of URTI in the same participants before and after a marathon, precluding a conclusive consensus. Besides the between-subjects effects, another important confounding factor in these results is the different pre and post follow-up time to track URTI. Objectives: Identify by meta-analysis whether a marathon Running increases the risk of URTI, adjusting the follow-up time to track URTI. Data sources: We searched for articles using MEDLINE (PubMed), Embase, Scopus, Web of Science, the Cochrane Library, and EBSCOhost, combining the marathon and respiratory infection descriptor synonyms, on 1st December 2022. Eligibility criteria: The PICOS framework included human population, comparison between pre and post marathon running, of URTI symptoms (assessed from one to 4 weeks), in noncontrolled intervention studies. Data Synthesis: Because follow-up was longer before the marathon in many studies, we adjusted the number of subjects with infections before marathon to the equivalent post-marathon follow-up duration. There was 18% higher incidence of URTI post-marathon (OR 1.18 95%CI [1.05-1.33], p= 0.005) in a very consistent meta-analysis (I2 = 0%, p = 0.69), with no risk of publication bias (Egger test p-value = 0.82) for the 7 studies included. The main issues with quality of the studies were bias in measuring the outcome, bias in classification of intervention (participation in the marathon) and time-varying confounding (corrected for analysis), and therefore the quality of evidence was moderate (GRADE approach = 3). Limitations: The need for follow-up time adjustment is a limitation, since the number of URTI recorded could be different if the original studies had used the same follow-up time pre and post marathon. The subjectivity of the URTI assessments is another limitation in this field. Conclusions: There is an increased risk of URTI post marathon running and research on this topic to understand mechanisms might support runners to find efficient interventions to reduce this risk. Protocol: Protocol registration on in the International Prospective Register of Systematic Reviews (PROSPERO): CRD42022380991.

The functions of leg muscles, structures and mechanisms in running.

The actions of the major human leg muscles are well established; however, the functions of these muscle actions during steady running remain unclear. Here, leg structures and mechanisms are considered in terms of their functions in meeting the task of a vehicle acting as an effective machine, supporting body weight during translation with low mechanical work demand and in supplying mechanical work economically. Legs are modelled as a sequence of linkages that predict muscle actions and reveal the varying muscle functions within the integrated leg. Work avoidance is achieved with isometric muscles and linkages that promote a sliding of the hip over the ground contact, resulting in an approximately horizontal path of the centre of mass. Economical work supply requires, for muscle with constrained power, shortening over the entire stance duration; this function is achieved by the hamstrings without disrupting the linkages resulting in work avoidance. In late stance, the two functions occur through coactivation of antagonistic muscles, providing one answer to Lombard's paradox. Quadriceps and hamstring tensions result in opposing moments about both hip and knee joints, but by doing so perform the independent yet complementary roles of work avoidance during translating weight support and economical work supply.

Comparison of bone mineral density of runners with inactive males: A cross-sectional 4HAIE study.

The purpose of the study was to determine whether running is associated with greater bone mineral density (BMD) by comparing the BMD of regularly active male runners (AR) with inactive nonrunner male controls (INC). This cross-sectional study recruited 327 male AR and 212 male INC (aged 18-65) via a stratified recruitment strategy. BMD of the whole body (WB) and partial segments (spine, lumbar spine (LS), leg, hip, femoral neck (FN), and arm for each side) were measured by dual-energy x-ray absorptiometry (DXA) and lower leg dominance (dominant-D/nondominant-ND) was established by functional testing. An ANCOVA was used to compare AR and INC. The AR had greater BMD for all segments of the lower limb (p<0.05), but similar BMD for all segments of the upper limb (p>0.05) compared with INC. Based on the pairwise comparison of age groups, AR had greater BMD of the ND leg in every age group compared with INC (p<0.05). AR had grater BMD of the D leg in every age group except for (26-35 and 56-65) compare with INC (p<0.05). In the youngest age group (18-25), AR had greater BMD in every measured part of lower extremities (legs, hips, femoral necks) compared with INC (p<0.05). In the 46-55 age group AR had greater BMD than INC (p < 0.05) only in the WB, D Leg, D neck, and ND leg. In the 56-65 age group AR had greater BMD than INC (p<0.05) only in the ND leg. Overall, AR had greater BMD compared with INC in all examined sites except for the upper limbs, supporting the notion that running may positively affect bone parameters. However, the benefits differ in the skeletal sites specifically, as the legs had the highest BMD difference between AR and INC. Moreover, the increase in BMD from running decreased with age.

How Humans Run Faster: The Neuromechanical Contributions of Functional Muscle Groups to Running at Different Speeds.

How the neuromechanics of the lower limb functional muscle groups change with running speed remains to be fully elucidated, with implications for our understanding of human locomotion, conditioning, and injury prevention. This study compared the neuromechanics (ground reaction and joint kinetics, kinematics and muscle activity) of middle-distance athletes running on an instrumented treadmill at six wide-ranging speeds (2.78-8.33 m·s-1). Ground reaction forces and kinematics were analyzed using inverse dynamics to calculate flexor and extensor joint torques, and positive and negative work done by these torques. Contributions of each functional muscle group to the total positive and negative work done by the limb during stance, swing, and the whole stride were quantified. During stance, the ankle plantar flexors were the major energy generator and absorber (>60%) at all speeds, but their contribution to whole stride energy generation and absorption declined with speed. Positive work by the hip extensors rose superlinearly with speed during stance (3-fold) and especially during swing (12-fold), becoming the biggest energy generator across the whole stride at >5 m·s-1. Knee flexor and extensor negative work also rose superlinearly with speed during swing, with the knee flexors becoming the greatest energy absorber over the whole stride at >7.22 m·s-1. Across speeds, plantar flexor peak moment and positive work accounted for 97% and 96% of the variance in step length, and swing hip extension peak moment and positive work accounted for 98% and 99% of the variance in step frequency. There were pronounced speed, phase (stance/swing), and work (positive/negative) dependent contributions of the different functional muscle groups during running, with extensive implications for conditioning and injury prevention.

Assessing Leg Blood Flow and Cardiac Output During Running Using Thermodilution.

Cardiac output (Q̇C) and leg blood flow (Q̇LEG) can be measured simultaneously with high accuracy using transpulmonary and femoral vein thermodilution with a single-bolus injection. The invasive measure has offered important insight into leg hemodynamics and blood flow distribution during exercise. Despite being the natural modality of exercise in humans, there has been no direct measure of Q̇LEG while running in humans. We sought to determine the feasibility of the thermodilution technique for measuring Q̇LEG and conductance during high-intensity running, in an exploratory case study. A trained runner (30 years male) completed two maximal incremental tests on a cycle ergometer and motorized treadmill. Q̇LEG and Q̇C were determined using the single-bolus thermodilution technique. Arterial and venous blood were sampled throughout exercise, with continuous monitoring of metabolism, intra-arterial and venous pressure, and temperature. The participant reached a greater peak oxygen uptake (V̇O2peak) during running relative to cycling (74 vs. 68 mL/kg/min) with comparable Q̇LEG (19.0 vs. 19.5 L/min) and Q̇C (27.4 vs. 26.2 L/min). Leg vascular conductance was greater during high-intensity running relative to cycling (82 vs. 70 mL/min/mmHg @ ~80% V̇O2peak). The "beat phenomenon" was apparent in femoral flow while running, producing large gradients in conductance (62-90 mL/min/mmHg @ 70% V̇O2peak). In summary, we present the first direct measure of Q̇LEG and conductance in a running human. Our findings corroborate several assumptions about Q̇LEG during running compared with cycling. Importantly, we demonstrate that using thermodilution in running exercise can be completed effectively and safely.

Monitoring fatigue state with heart rate-based and subjective methods during intensified training in recreational runners.

The purpose of this study was firstly to examine the sensitivity of heart rate (HR)-based and subjective monitoring markers to intensified endurance training; and secondly, to investigate the validity of these markers to distinguish individuals in different fatigue states. A total of 24 recreational runners performed a 3-week baseline period, a 2-week overload period, and a 1-week recovery period. Performance was assessed before and after each period with a 3000m running test. Recovery was monitored with daily orthostatic tests, nocturnal HR recordings, questionnaires, and exercise data. The participants were divided into subgroups (overreached/OR, n = 8; responders/RESP, n = 12) based on the changes in performance and subjective recovery. The responses to the second week of the overload period were compared between the subgroups. RESP improved their baseline 3000 m time (p < 0.001) after the overload period (-2.5 ± 1.0%), and the change differed (p < 0.001) from OR (0.6 ± 1.2%). The changes in nocturnal HR (OR 3.2 ± 3.1%; RESP -2.8 ± 3.7%, p = 0.002) and HR variability (OR -0.7 ± 1.8%; RESP 2.1 ± 1.6%, p = 0.011) differed between the subgroups. In addition, the decrease in subjective readiness to train (p = 0.009) and increase in soreness of the legs (p = 0.04) were greater in OR compared to RESP. Nocturnal HR, readiness to train, and exercise-derived HR-running power index had ≥85% positive and negative predictive values in the discrimination between OR and RESP individuals. In conclusion, exercise tolerance can vary substantially in recreational runners. The results supported the usefulness of nocturnal HR and subjective recovery assessments in recognizing fatigue states.

Effect of changes in motor skill induced by educational video program to decrease lower-limb joint load during cutting maneuvers: based on musculoskeletal modeling.

BACKGROUND: This study investigated the effects of changes in motor skills from an educational video program on the kinematic and kinetic variables of the lower extremity joints and knee ligament load. METHODS: Twenty male participants (age: 22.2 ± 2.60 y; height: 1.70 ± 6.2 m; weight: 65.4 ± 7.01 kg; BMI: 23.32 ± 2.49 [Formula: see text]) were instructed to run at 4.5 ± 0.2 m/s from a 5 m distance posterior to the force plate, land their foot on the force plate, and perform the cutting maneuver on the left. The educational video program for cutting maneuvers consisted of preparatory posture, foot landing orientation, gaze and trunk directions, soft landing, and eversion angle. The measured variables were the angle, angular velocity of lower extremity joints, ground reaction force (GRF), moment, and anterior cruciate ligament (ACL) and medial collateral ligament (MCL) forces through musculoskeletal modeling. RESULTS: After the video feedback, the hip joint angles increased in flexion, abduction, and external rotation (p < 0.05), and the angular velocity increased in extension (p < 0.05). The ankle joint angles increased in dorsiflexion (p < 0.05), and the angular velocity decreased in dorsiflexion (p < 0.05) but increased in abduction (p < 0.05). The GRF increased in the anterior-posterior and medial-lateral directions and decreased vertically (p < 0.05). The hip joint moments decreased in extension and external rotation (p < 0.05) but increased in adduction (p < 0.05). The knee joint moments were decreased in extension, adduction, and external rotation (p < 0.05). The abduction moment of the ankle joint decreased (p < 0.001). There were differences in the support zone corresponding to 64‒87% of the hip frontal moment (p < 0.001) and 32‒100% of the hip horizontal moment (p < 0.001) and differences corresponding to 32‒100% of the knee frontal moment and 21‒100% of the knee horizontal moment (p < 0.001). The GRF varied in the support zone at 44‒95% in the medial-lateral direction and at 17‒43% and 73‒100% in the vertical direction (p < 0.001). CONCLUSIONS: Injury prevention feedback reduced the load on the lower extremity joints during cutting maneuvers, which reduced the knee ligament load, mainly on the MCL.

Exploring the Influence of Acid-Base Status on Athletic Performance during Simulated Three-Day 400 m Race.

This study aimed to investigate the ability of highly trained athletes to consistently perform at their highest level during a simulated three-day 400 m race and to examine the impact of an alkaline diet associated with chronic consumption of bicarbonate-rich water or placebo on their blood metabolic responses before and after the three races. Twenty-two highly trained athletes, divided into two groups-one with an alkalizing diet and placebo water (PLA) and the other with an alkalizing diet and bicarbonate-rich water (BIC)-performed a 400 m race for three consecutive days. Performance metrics, urine and blood samples assessing acid-base balance, and indirect markers of neuro-muscular fatigue were measured before and after each 400 m race. The evolution of the Potential Renal Acid Load (PRAL) index and urinary pH highlights the combination of an alkalizing diet and bicarbonate-rich hydration, modifying the acid-base state (p < 0.05). Athletes in the PLA group replicated the same level of performance during three consecutive daily races without an increase in fatigue-associated markers. Athletes experienced similar levels of metabolic perturbations during the three 400 m races, with improved lactate clearance 20 min after the third race compared to the first two (p < 0.05). This optimization of the buffering capacity through ecological alkaline nutrition and hydration allowed athletes in the BIC group to improve their performance during the third 400 m race (p < 0.01). This study highlights athletes' ability to replicate high-level performances over three consecutive days with the same extreme level of metabolic disturbances, and an alkaline diet combined with bicarbonate-rich water consumption appears to enhance performance in a 400 m race.