Modeling record scores in the snatch and its variations in the long-term training of young weightlifters.

The primary aim of the current study was to determine the time curves of changes in the record scores in the snatch and its variations during a two-year training cycle in young weightlifters. This study also aimed at assessing the ratios between these scores and at predicting the snatch record scores at the end of the subsequent annual training macrocycle. The final purpose was to compare the record scores with the isometric peak torque values of the trunk and knee extensors. The study involved 16 weightlifters who were tested seven times at three-month intervals. The overall mean ratios of the record scores in the hang snatch to those in the snatch and the record scores in the hang power snatch to those in the snatch were approximately constant and amounted to 0.95 and 0.79, respectively. The overall mean ratio between the scores in the power snatch to those in the snatch was approximately 0.88. Statistically significant differences (p < 0.05) between the individual time trajectories of record scores in the snatch and its derivatives were identified in two consecutive annual training macrocycles. The error in predicting record results at the end of the following annual training macrocycle was 6.7 ± 4.7% or 8.1 ± 3.4% depending on the way the measurement data were modeled. The results of the study also indicate that the measurements of the isometric peak torque of the trunk extensors performed in laboratory conditions can be useful in diagnosing the strength capacity of young weightlifters.

Variability of shoulder girdle temperature in the initial phase of the snatch in weightlifting.

PURPOSE: The identification of activation, synchronization and work of individual muscles in the subsequent stages of lifting weights is interesting for researchers and trainers. Unfortunately, the existing methods of research do not provide such possibilities. Such information could be gathered from infrared measurements as they are non-invasive and can be carried out without the direct involvement of the weightlifter. The purpose of the study was to analyse temperature changes in the shoulder girdle in the first phase of the snatch in weightlifting. METHODS: The study involved 11 weightlifters who competed in two weight categories, 94 and 105 kg, during the World University Championships in 2018. The performance of the snatch was recorded using a thermographic camera in three consecutive attempts. We analysed the temperature changes in the left and right shoulder girdles in the two initial stages of the snatch. Statistical analysis of empirical data was performed using linear mixed effects models. RESULTS: Statistically significant temperature increases were found from the moment of gripping the barbell to the moment it was pulled. These effects were different in individual weightlifters, but did not depend on the attempt or the side of the body. CONCLUSIONS: Temperature increases in the initial phase of the snatch are most likely the result of activating successive motor units in order to perform the effort needed to pull the barbell and cause it to accelerate. The results obtained confirm that thermography is an effective method of monitoring muscle activity in weightlifting, which may be useful for coaches and athletes.

Changes in electromyographic signals and skin temperature during standardised effort in volleyball players.

PURPOSE: The state of athletes' muscles is not constant, but it differs depending on the stage of sports training, which is associated with different degrees of muscle fatigue. There is thus a need to find a non-invasive and simple method to assess muscle fatigue. The aim of the study was to determine the relationship between muscle fatigue due to physical effort and changes in skin temperature, measured using a thermographic camera. METHODS: The study involved 12 volleyball players. The participants were to maintain 70% of peak torque in the joint for as long as possible. We measured peak torque and the time of maintaining 70% of its value (tlim) as well as continuously recording skin temperature and electromyographic (EMG) signals in the region of the belly of the rectus femoris. The measurements were taken twice: before and after a series of squats. RESULTS: The study found that tlim decreased when isometric contraction was per- formed after physical effort. Pre- and post-exercise skin temperature did not differ significantly, however, the increase rates of tempera- ture and the root mean square (RMS) of the EMG signals grew significantly. In most of the players, skin temperature also correlated with the RMS, median frequency (MDF), and mean frequency (MF) of the EMG signals. CONCLUSIONS: Measuring the time of maintaining submaximal torque during isometric contraction and the slope coefficient for the increase in temperature recorded using a thermographic camera can be a simple, cost-effective, and non-invasive method of assessing fatigue and efficiency decreases in the muscles in volley- ball players.

Using the discrete wavelet transform in assessing the effectiveness of rehabilitation in patients after ACL reconstruction.

PURPOSE: The purpose of the current study was to assess the effectiveness of rehabilitation in patients after anterior cruciate ligament reconstruction (ACLR) using a wavelet analysis of the torque-time curve patterns of the extensors of the affected knee. The analysis aimed at the quantitative evaluation of irregularities in these torque-time patterns. METHODS: The study involved a group of 22 men who had had ACL reconstruction. The torque-time characteristics were recorded 3, 6 and 12 months after the surgery by an isokinetic dynamometer. They were then examined using the orthogonal Daubechies 4 (Db 4) and biorthogonal Bior 3.1 wavelets. RESULTS: A statistical analysis of the results revealed significant differences in values of the high-frequency energy stored in the details of the signal from the dynamometer between the first and last measurements, both for the Db 4 ( p ≤ 0.023) and Bior 3.1 ( p ≤ 0.01) wavelets. These differences were found in 73% of patients whose curve patterns were analysed using the Db 4 wavelet and in 82% of patients in the case of the Bior 3.1 wavelet. CONCLUSIONS: The wavelet transform proved to be an effective research tool in the qualitative evaluation of irregularities occurring in the curve patterns of the torque generated by the extensors of the ACL reconstructed knee. The findings of the study suggest that time-frequency analyses of these characteristics can be of practical importance, as they help assess the state of the patient's knee joint and his progress in rehabilitation after ACLR.