ECSS Paris 2023: CP-BM11
INTRODUCTION: A growing number of people prefer gym instead of sports practice. In the long term, the practice of activities in which there is a lack of a decision-making process associated with rapid whole-body movement could influence physical performance. The study aim was to investigate the differences in a time reaction task (TRT) between a sportive, a sedentary, and a gym user group. METHODS: A total of 80 participants were recruited. Only 18 participants met the eligibility criteria and presented a complete EMG data set. The control group (CG) (3 females, 3 males, 24 ± 2.1 years, 171.5 ± 9.8 cm, 75.7 ± 19 kg) was composed of sedentary people. The sports group (SG) (6 men, 21.8 ± 2.3 years, 178.7 ± 5.2 cm, 73.1 ± 6.7 kg) was composed of people practicing soccer or basketball. The gym group (GG) (2 females, 4 males, 21.2 ± 1.5 years, 171 ± 6.9 cm, 67.5 ± 8.6 kg) was composed of gym users. For the SG and GG, the participants had to perform at least 360 min/week. All groups performed a TRT in which they had to react to a stimulus with a jump for 3 times. Was recorded the time between the stimulus and the jump. Furthermore, s-EMG was recorded for the tibialis anterior (TA) and gastrocnemius lateralis (GL) during the task. A maximal voluntary contraction was recorded before the time reaction task to normalize data (MVC%). Data were analyzed with the Friedman and the Durbin-Conover comparison to detect differences between the groups. The Spearman correlation analysis was used to detect the correlation between body fat percentage (%F) and the variables studied. RESULTS: No significant statistical differences were detected between the CG (mean (m) 0.54±0.08 s), the SG (m 0.5±0.13 s) and the GG (m 0.56±0.08 s), and between the SG and GG. A significant difference was detected between the TA of the CG (m 3.93±1.61 MVC%) and the SG (m 1.43±0.13 MVC%) (p=0.004) and between the SG and the GG (m 2.08±0.6 MVC%) (p=0.034). No significant difference was detected between CG and GG, and among GL and CG (m 8.20±5.23 MVC%) and the SG (m 5.76±3.39 MVC%), between CG and GG (m 9.96±5.23 MVC%), and between SG and GG. After the correlation analysis, no significant difference was detected in most of the variables. Was found correlation between the % of activation of the TA and the %F, total (correlation coefficient (CC) 0.585; p=0.011), of the right (CC 0.622; p=0.006) and of the left leg (CC 0.621; p=0.006). This was also confirmed by the regression model built with % tibial activation as the dependent and total and limb fat as independent variables. CONCLUSION: The results show a less active TA and GL for the SG but a better performance in the TRT. Was verified that practicing a sport increases the quality of neuromuscular action, suggesting sporting activity as a more effective tool for agility. These preliminary findings could be important as the current generation of gym-goers gets older, in some everyday tasks. Future studies should consider these findings in older adults from a retrospective point of view.
Read CV Luca PetrignaECSS Paris 2023: CP-BM11
INTRODUCTION: The Rear-foot-elevated split squat (RFESS) is a typical unilateral exercise[1, 2]. Previous studies have shown that the RFESS not only equally improve strength levels but also have superior effects on enhancing change of direction and single-leg jumping performance compared to the back squat, [3-5]. Identifying the change of muscle activation and ground reaction force distribution is important in needs analysis of the RFESS, Knowledge of that can be used to guide the design of the resistance training program.However, there is currently a lack of research on the muscle activation and GRF of the RFESS under different loads and fatigue levels. Therefore, the purpose of this study is to explore the changes in muscle activation and GRF of RFESSs with the changes of loads and fatigue levels. METHODS: 19 male college athletes (RFESS 1RM: left leg, 103.06±13.3 kg; right leg, 103.61±13.15 kg) attended five experimental sessions. During the session 1 and 2, anthropometric data (height, weight) were collected, and the participants were familiarized with the testing procedures. In the testing session 3 and 4, the 1RM of RFESS was tested, followed by randomized testing of 75% 1RM fatigue-to-failure and different loads (40%,50%,60%,70%,80%,90%1RM). surface electromyographic (EMG), kinetic and three-dimensional kinematic data were collected during the tests. Two-factor repeated measures ANOVA was used to determine differences of GRF, GRF ratio, and average surface electromyographic （AEMG）% between different loads and fatigue level (initial, middle, and final stages of fatigue to failure set) on the lead and rear foot. The overall alpha level was set at p ≤0.05. RESULTS: The GRF (GRF) of the front leg during the RFESS significantly increased from 40% to 90% 1RM (p = 0.001) and was consistently higher than that of the back leg (p = 0.001). The AEMG% of the vastus lateralis of the front leg was the highest, followed by the vastus lateralis of the rear leg, gluteus maximus of the front leg, and biceps femoris of the front leg. the proportion of GRF on the rear leg decreased as the load increased. The ratio of GRF between the front and rear legs was approximately 8:2. As the fatigue level up, the AEMG% of the main muscles of both the front and rear legs showed no significant changes across the initial, middle, and final stages of fatigue to failure set (p > 0.05). the GRF of the front leg showed an increasing trend across the initial, middle, and final stages. The GRF in the initial stage was significantly lower than that in the middle stage (p = 0.003) and final stage (p = 0.001), while there was no significant difference between the middle and final stages (p = 0.19). CONCLUSION: Muscle Activation and GRF are affected by loads and fatigue levels during the RFESS. The front leg is the main force contributor (80%), and the loads and fatigue level have little effect on the contribution of the front legs to the force during RFESS exercises.
Read CV Kaifang LiaoECSS Paris 2023: CP-BM11
INTRODUCTION: Landing requires athletes to attenuate ground reaction forces in three planes while establishing postural stability. Various jump or landing tasks are employed to monitor performance and injury risks. These include the Drop Landings (DL); Drop Jumps (DJ) and Countermovement Jumps (CMJ). Moreover, landing stability can be quantified using Dynamic Postural Stability Indices (DPSI) and Time to Stabilisation (TTS). The study purpose was to evaluate the stability indices of landing phases across the various landing conditions. METHODS: 20 female recreational athletes (age: 23.4 ± 2.87 years; mass: 62.85 ± 10.28 kg; height: 1.69 ±0.08 m) volunteered to complete 40cm DL, 40cm DJ and CMJ in a randomised order. All kinetics were recorded using two Bertec force plates at 1000Hz. Force tracings were analysed in MatLab, where stability metrics (APSI, MLSI, VSI, DPSI and TTS) were calculated. One-way ANOVA with appropriate post-hoc tests were conducted with significance at p<0.05. RESULTS: Stability indices showed differences across all three landings and directional components (p<0.001). Higher APSI were recorded for DL (0.059 ± 0.013) compared to DJ (0.027 ± 0.025) and CMJ (0.019 ± 0.013) and a lower MLSI in DL (0.023 ± 0.01) compared to CMJ (0.032 ± 0.015). VSI and DPSI were the lowest in DL (0.265 ± 0.068; 0.273 ± 0.07) compared to DJ (0.578 ± 0.175; 0.564 ± 0.148) and CMJ (0.514 ± 0.136; 0.516 ± 0.136). Finally, no TTS differences were observed across the landings (DL: 1.50 ± 0.27s; DJ: 1.52 ± 0.35s; CMJ: 1.40 ± 0.28s). CONCLUSION: Stability differences were noted across the various conditions, with the DL reporting the most differences with DJ and CMJ. It’s apparent that DJ and CMJ are more dynamic movements and more variable in terms of joint movements (1). Furthermore, studies have shown that cognitive load can negatively impact knee joint stability during landing tasks (2), showing that dual-task conditions can significantly increase peak GRF. This may translate into the findings of the current study, where VSI and DPSI are significantly larger in DJ and CMJ compared to DL. Additionally, DJ and CMJ require more reactive landings compared to DL. APSI in DL may indicate a greater joint excursion as most of the force attenuation occurs in the AP and vertical planes. Specific to the vertical stability (VSI & DPSI) differences might be attributed to the landing heights, leading to greater joint flexion angles and higher GRF (3). In conclusion, Landing stability may be determined by the dynamics of the jump or preceding events. Additionally, postural stability might be affected by the landing height and kinematic strategies used to attenuate force. References: 1 González-García et al. Appl Sci. 2024;14(6):2662. 2 McCarren et al. Mil Med. 2023;188(7-8): e2102–e2108. 3 Verniba et al. Sports Med Open. 2017;3: 6.
Read CV Andrew GreenECSS Paris 2023: CP-BM11