Changes in voluntary and electrically induced contractions during strength training and detraining

To elucidate the changes in neuro-muscular function during strength training and detraining, five male subjects underwent progressive isotonic strength training of their calf muscles three times a week for 8 weeks with additional detraining for the same periods. Electrically evoked twitch contractions were induced in the triceps surae muscles of each subject every 4 weeks during the training and detraining periods. At the same time, maximal voluntary isometric contractions (MVC) and the maximal girth of the calf (MGC) were measured. During the training period, MVC increased significantly from 98.4 to 129.6 Nm (31.7%, P less than 0.01) for the first 4 weeks of training but MGC showed little increase. Neither of the changes correlated with each other. Twitch contraction parameters, i.e. maximal twitch torque (Pt), maximal rate of torque development (max dT/dt) and rate of relaxation (relax dT/dt) showed no statistical change. During detraining, on the contrary, a large and significant increase (22.5%, P less than 0.01) was observed in max dT/dt without any changes in Pt and relax dT/dt. The MVC/Pt showed both significant increases during training and decreases during detraining. Our data suggest that short term strength training as employed in the present study does not induce changes in the contractile properties of the muscle during training, but may significantly affect the rate of force development during the subsequent detraining period, indicating the possible existence of complex post-training muscle adaptation.     

Effects of exercise cessation on lipids and lipoproteins in distance runners and power athletes

The purpose of this study was to determine the effects of short-term exercise cessation on lipid and lipoprotein profile and insulin sensitivity in highly trained runners (n=12; mean age 19.9 years) and power athletes (n=12; mean age 24.4 years). Following 14 days of exercise cessation, running time to exhaustion and maximal oxygen uptake decreased by 9.2% and 4.8% (P < 0.05) in the runners, while in the power athletes one repetition maximum squat and bench press did not change (P>0.05). No changes occurred in body composition. Data from a 2-h oral glucose tolerance test revealed an impairment of the glycemic state in all athletes (P<0.05). In contrast, exercise cessation did not significantly (P>0.05) alter plasma levels of cholesterol, triglycerides, and low density (LDL) and high density lipoprotein (HDL). No changes were observed in HDL₂, HDL_2b, and HDL₃ subfractions, LDL diameter, and qualitative LDL pattern (P>0.05). These data thus suggest that despite a decrease in insulin sensitivity, short-term exercise cessation, independent of exercise mode, was insufficient to alter plasma lipid and lipoprotein profiles in well-trained athletes.     

Impact of COVID-19 lockdown on match activity and physical performance in professional football referees

To investigate the effect of COVID-19 lockdown on match-play metrics in professional football referees during official matches of the Spanish professional leagues. Forty-two professional football referees from the First (n = 20) and Second Division (n = 22) were monitored during 564 official games using Global Positioning System (GPS) technology. Data of matches before lockdown were compared to matches after resumption of the competition. Compared to pre-lockdown, in the referees of the First Division there was a decrease in the total running distance and the distance covered at all speed thresholds > 6 km · h^-1 after lockdown (P < .05). In the Second Division referees, the post-lockdown measurement only showed a decrease in the running distance at 21–24 km · h^-1 (P < .05), with no changes in the other speed thresholds. The post-lockdown measurement showed an increased distance covered at < 6 km · h^-1 and the number of accelerations for both First and Second Division referees (P < .05). Referees’ match activity was reduced due to the COVID-19 lockdown, while the effect on running parameters was more pronounced in First Division referees.     

The effects of COVID-19 lockdown on jumping performance and aerobic capacity in elite handball players

The aim of this research was to analyse the capacity of a home-based training programme to preserve aerobic capacity and jumping performance in top-level handball players during the COVID-19 lockdown. Eleven top-level male handball players from the same team participated in the study. A submaximal shuttle run test and a counter-movement jump test were used to measure the players’ aerobic fitness and lower limb explosive strength, respectively. A 9-week home-based training programme was followed during lockdown. Pre-test measurements were assessed before the pandemic on 29 January 2020 and ended on 18 May 2020. Moderate significant mean heart rate increases were found in the late stages of the submaximal shuttle run test after the lockdown (stage 5, 8.6%, P = 0.015; ES = 0.873; stage 6, 7.7%, P = 0.020; ES = 0.886; stage 7, 6.4%, P = 0.019; ES = 0.827). Moderate significant blood lactate increases were observed immediately after the submaximal shuttle run test following the lockdown (30.1%, P = 0.016; ES = 0.670). In contrast, no changes were found in jump performance. A structured home-based training programme during the COVID-19 lockdown preserved lower limb explosive strength but was an insufficient stimulus to maintain aerobic capacity in top-level handball players.     

Adipocyte responses to adrenaline and insulin in active and former sportsmen

The rates of lipolysis and lipogenesis in adipocytes, isolated from biopsy samples of subcutaneous fat, was assessed by estimation of glycerol release during a 30-min incubation, and of the incorporation of 14C-glucose into lipids during a 1-h incubation at 37 degrees C, respectively. The subjects were six highly-qualified, active endurance sportsmen, eight former endurance sportsmen of international class, and six untrained young men. In the active sportsmen the basal rate of lipolysis was about half of that in the previously-active sportsmen and the untrained subjects, but after the addition of adrenaline (10(-4) or 5 x 10(-4) mol.l-1) the lipolysis rate was the highest. No differences were observed in the lipolytic rates in the former sportsmen compared to the untrained subjects. Gases of a comparatively high level of lipogenesis were found in the trained subjects. The addition of insulin (9 microU.ml-1) to isolated adipocytes caused a significant augmentation of individual rates of lipogenesis in the active sportsmen and the untrained persons but not in the previously-active sportsmen. In comparison with the active sportsmen, the previously active sportsmen revealed an increased basal rate of lipolysis and a reduced sensitivity to the lipogenic action of insulin. These findings suggest that these changes may have had significance in avoiding an increase of adipose tissue after a decrease in energy expenditure due to a change in physical activity.