Effects of contraction duration on low-frequency fatigue in voluntary and electrically induced exercise of quadriceps muscle in humans

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMGrms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMGrms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise

Heavy-resistance training in older Scandinavian men and women: short- and long-term effects on arm and leg muscles

The short- and long-term effects of heavy-resistance training (85% of one-repetition maximum (RM)) on elbow flexion and knee extension dynamic and isokinetic strength and on morphology in the biceps brachii and vastus lateralis muscles were evaluated during 1 year in 35 Scandinavian men and women, aged 70-77 years, 12 of whom formed a control group. After the first 11 weeks of training (n = 23; 3 times/week) elbow flexion and knee extension dynamic strength (1 RM) had increased [mean +/- SD] 49% +/- 16 and 163% +/- 75, respectively, with no significant difference between men and women. For the following 27 weeks, strength was maintained with one training session per week (n = 12) but dropped without training (n = 11). After the final 11 weeks of training (n = 11; 3 times/week), strength had further increased 32% +/- 16 in both the arm and the leg. Isokinetic strength measurements (Cybex II; 30 degrees/s) revealed similar but smaller gains than for dynamic strength. Muscle biopsies (n = 20) taken at the start and after the first 11 weeks of training showed a significant increase in the area of both type 1 and type 2 fibers in the biceps brachii muscle and a positive significant correlation between the percentage increase in the proportional area of type 2 fibers in the vastus lateralis muscle and the percentage increase in knee extension dynamic muscle strength. In conclusion, older Scandinavian men and women have a high capacity both to improve and to maintain muscle strength, some of which is mediated through an adaptation in the muscle fiber type population

Incidence and burden of injury at the Tokyo 2020 Paralympic Games held during the COVID-19 pandemic : A prospective cohort study of 66 045 athlete days

Objective To describe the epidemiology of injuries at the Tokyo 2020 Paralympic Games, including injuries sustained in the new sports of badminton and taekwondo. Methods Injury data were obtained daily via the established web-based injury and illness surveillance system (WEB-IISS; 81 countries, 3836 athletes) and local organising committee medical facilities (81 countries, 567 athletes). Univariate unadjusted incidences (injuries per 1000 athlete days with 95% CIs), injury proportion (IP, %) and injury burden (days lost per 1000 athlete days) are reported. Results A total of 4403 athletes (1853 women, 2550 men) from 162 countries were monitored prospectively during the 3-day pre-competition and 12-day competition periods (66 045 athlete days). 386 injuries were reported in 352 athletes (IP=8.0%) with an incidence of 5.8 per 1000 athlete days (95% CI 5.3 to 6.5). Football 5-a-side (17.2), taekwondo (16.0), judo (11.6) and badminton (9.6) had the highest incidence. There was a higher incidence of injuries in the pre-competition period than in the competition period (7.5 vs 5.4; p=0.0053). Acute (sudden onset) injuries and injuries to the shoulder (0.7) and hand/fingers (0.6) were most common. Injury burden was 10.9 (8.6-13.8), with 35% of injuries resulting in time loss from training and competition. Conclusion Compared with previous Paralympic Games, there was a reduction in injury incidence but higher injury burden at the Tokyo 2020 Paralympic Games. The new sports of taekwondo and badminton had a high injury incidence, with the highest injury burden in taekwondo, compared with other sports. These findings provide epidemiological data to inform injury prevention measures for high-risk sports

Incidence and burden of illness at the Tokyo 2020 Paralympic Games held during the COVID-19 pandemic : a prospective cohort study of 66 045 athlete days

OBJECTIVE : To describe the incidence and burden of illness at the Tokyo 2020 Paralympic Games, which was organised with strict COVID-19 countermeasures. METHODS : Daily illnesses were recorded via the web-based injury and illness surveillance system (teams with their own medical staff; n=81), and local polyclinic services (teams without their own medical staff; n=81). Illness proportion, incidence and burden were reported for all illnesses and in subgroups by sex, age, competition period, sports and physiological system. RESULTS : 4403 athletes (1853 female and 2550 male) from 162 countries were monitored for the 15-day period of the Tokyo Paralympic Games (66 045 athlete days). The overall incidence of illnesses per 1000 athlete days was 4.2 (95% CI 3.8 to 4.8; 280 illnesses). The highest incidences were in wheelchair tennis (7.1), shooting (6.1) and the new sport of badminton (5.9). A higher incidence was observed in female compared with male athletes (5.1 vs 3.6; p=0.005), as well as during the precompetition versus competition period (7.0 vs 3.5; p1 day. CONCLUSION : The incidence of illness at the Tokyo 2020 Paralympic Games was the lowest yet to be recorded in either the summer or winter Paralympic Games. Dermatological and respiratory illnesses were the most common, with the burden of respiratory illness being the highest, largely due to time loss associated with COVID-19 cases. Infection countermeasures appeared successful in reducing respiratory and overall illness, suggesting implementation in future Paralympic Games may mitigate illness risk.http://bjsm.bmj.comhj2023Sports Medicin