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Background: The aim of this study was to analyze muscle injuries and their related risk factors during the Athletics events of the 2020 Tokyo Olympic Games including the differences in muscle injury rates between heats and finals., Methods: We included and analyzed in this study muscle injuries diagnosed by either magnetic resonance imaging, ultrasound, or physical examinations by at least two physicians, from Athletics athletes participating at the 2020 Tokyo Olympic Games. Data from electronic medical records, including sex, nationality, event, and the round (heat vs. final) during which the muscle injury occurred and the air temperature in the stadium, measured every five minutes during the competition were extracted., Results: Among the 1631 athletes who competed, a total of 36 athletes (20 males and 16 females) were diagnosed with a muscle injury during the 2020 Tokyo Olympic Games. Among them, 24 occurred during heats (1.47 per 100 athletes) and 12 during finals (2.20 per 100 athletes) (P=0.25). Logistic regression analysis revealed that the geographic region of athletes' origin was a factor associated with muscle injury, with the highest muscle injury rate being in athletes from Africa (odds ratio [OR]=4.74, 95% confidence interval [CI]) = 1.75 to 12.82) and North America (OR=3.02, 95%CI=1.27 to 7.20). For male athletes, competing in finals was a risk factor to sustain a muscle injury (OR=2.55, 95%CI=1.01 to 6.45)., Conclusions: During the 2020 Olympic Games, muscle injury rate was higher in finals than in heats, reaching statistical significance in male athletes.

Over the last 50 years, the development of running shoes has been mainly focused on improving the protection and comfort of the runner and her/his foot. Although there have been tentative attempts by companies to make shoes a tool for improving athletic performance, this goal has only recently been achieved. Indeed, the year 2016 was a real turning point when Nike launched its first shoe benefiting from the advanced footwear technology. Advanced footwear technology (AFT) mostly consists of an increased sole thickness, a curved and stiff plate embedded or below the shoe midsole, and an outsole with a marked concave shape. This innovation turned to a game changer in the world of distances running performance. Indeed, between 2016 and 2019, many male and female runners broke personal best times, national records, area, and world records in distance from 5 km to the marathon. The present article aimed at describing the magnitude of these performance enhancements in distance running as well as and the possible underlying performance-enhancement mechanisms associated with the advanced footwear technology. It also reviewed the existing literature on the safety aspects of "classical" construction shoes and AFT shoes. It concluded on a possible shoe mechanical tests-based protocol to maintain fair distance running competitions while not totally preventing manufacturers to innovate, and some thoughts on the nature and goals of further studies to be conducted to assess the safety (macro- and micro-traumatic) AFT in both elite and recreational runner populations.

Background: To investigate the effects of strength exercise and training on the natural killer cell counts in elderly humans., Methods: The study examined strength exercise-induced changes in the number of NK cells and changes in stress hormones in 16 sedentary elderly subjects before and after a 8-week strength training intervention. Blood samples were obtained before, immediately and 6 hours after a standardized strength test. Blood samples were also obtained from ten sedentary young subjects, under the same conditions and from ten resting elderly subjects serving as time controls., Results: Prior to training, older adults immediately decreased (from 165.4+/-19.5 microL to 110.6+/-14.3 microL; mean+/-SEM) their NK cell count in response to the standardized strength test, whereas young controls increased their count (from 157.6+/-28.8 microL(-1) to 241.4+/-39.8 microL(-1)). After strength training, the same old subjects slightly increased (from 159+/-19.8 microL(-1) to 166.6+/-19.7 microL(-1)) their NK cell counts in response to the standardized strength test. In elderly subjects, no increase in stress hormone was observed following the strength test either before or after the strength training programme., Conclusions: The results suggest that in sedentary older adults, unlike young subjects, strength exercises can induce a transient decrease in NK cell count which can be cancelled by a short-term strength conditioning. Therefore, caution should be taken regarding immunocompetence of older adults when initiating a rehabilitation programme based on strength.

Background: We sought to determine the effects of a long distance triathlon (4 km swim, 120 km bike-ride, and 30 km run) on the four-day kinetics of the biochemical markers of muscle damage, and whether they were quantitatively linked with muscle function impairment and soreness., Experimental Design: Data were collected from 2 days before until 4 days after the completion of the race., Participants: Twelve triathletes performed the triathlon and five did not., Measures: Maximal voluntary contraction (MVC), muscle soreness (DOMS) and total serum CK, CK-MB, LDH, AST and ALT activities were assessed., Results: Significant changes after triathlon completion were found for all muscle damage indirect markers over time (p < 0.0001). MVC of the knee extensor and flexor muscles decreased over time (p < 0.05). There is disparity in the time point at which peak values where reached for DOMS, MVC and enzyme leakage. There is no correlation between serum enzyme leakage, DOMS and MVC impairment which occur after triathlon., Conclusions: Long distance triathlon race caused muscle damage, but extent, as well as muscle recovery cannot be evaluated by the magnitude of changes in serum enzyme activities. Muscle enzyme release cannot be used to predict the magnitude of the muscle function impairment caused by muscle damage.

Background: The purpose of this study was to assess the validity of a new device to evaluate isometric strength during multi-joint exercise such as the squat or bench press., Methods: The device used an electric motor-driven bar to simultaneously generate and measure forces during weight lifting exercises. This new device and a force platform measured the forces generated by either the motor on a fixed telescopic steel girder (passive condition) or a subject pushing vertically against the bar from three squat positions (active condition). In the passive condition, 252 measurements were made, with 3 trials for 6 bar heights and 14 bar loads. In the active condition, 8 young physically active students (age, height and body mass were 25.1 +/- 2.6 years, 179.3 +/- 7.2 cm and 82.0 +/- 9.9 kg, respectively) performed 3 maximal isometric strength (MIS) trials in each of the 3 squat exercise positions (parallel, half and quarter squat), and 3 additional MIS trials in one position randomly assigned two weeks later to test inter-day reliability., Results: In the passive condition, no differences were observed between the forces measured by the force platform and the new device. The coefficient of linear regression (r) and the coefficient of variation (CV) were 1 and below 0.23%, respectively. In the active condition, the peak MIS measured was 2828 N and the values of r and CV were above 0.982 and below 5.96%, respectively. The assessment of inter-day reliability showed an r value of 0.984 and a CV of 3.98%., Conclusions: This study demonstrated that the new electric motor-driven exerciser provides valid and reliable data when used to generate forces and measure isometric strength throughout the load and motion ranges commonly used in squat exercise.