Examining the association between speed and myoelectric activity: Time-based differences and muscle group balance.

The purpose of this study is to investigate the relationship between speed and myoelectric activity, measured during an incremental 25m shuttle running test, exploring the time-based variations and assessing muscle group balance within the context of this association. Twelve male young soccer players (n = 12) aged 18±1.2 years, with an average body mass of 68.4±5.8kg and average body height of 1.72±0.08m, from a professional Italian youth team (Italian "Primavera"), volunteered as participants for this study. The speed of each player during testing was measured using GPS technology, sampling at 50Hz. Myoelectrical activities of the gluteus, hamstrings, and quadriceps muscles were recorded through wearable sEMG devices, sampled at 100Hz. To ensure alignment of the sampling frequencies, the sEMG data was resampled to 50Hz, matching the GPS data sampling rate. This allowed for direct comparison and analysis of the data obtained from both measurement systems. The collected data were then analyzed to determine the relationship between the investigated variables and any potential differences associated with different sides of the body. The results revealed a robust correlation (r2≈0.97) between the speed of the participants (m·s-1) and their myoelectrical activity (µV) during the test. Factorial ANOVA 2x11 showed no significant differences between the sides of the analyzed muscles (p>0.05). The interpolation lines generated by the association of speed and sEMG exhibit very similar angular coefficients (0.9 to 0.12) in all six measurements obtained from electromyography of the three investigated muscle groups on each side of the body. In conclusion, the concurrent validity between the two instruments in this study indicates that GPS and sEMG are valid and consistent in estimating external load and internal load during incremental shuttle running.

Hypertrophic adaptations to a 6-week in-season barbell vs. flywheel squat added to regular soccer training.

BACKGROUND: The aim of this study was to compare the hypertrophic adaptations to barbell or flywheel squat exercise added to regular in-season soccer training. METHODS: Quadriceps' (rectus femoris [RF], vastus medialis [VM] and vastus lateralis [VL]) cross-sectional area (CSA) in its portions (proximal [PROX], middle [MID], and distal [DIST]) was measured on both legs before and after a 6-week barbell (80 to 90% one-maximum repetition; N.=7) or flywheel (0.0611 to 0.0811 kg·m2; N.=7) in an U19 professional soccer team using a 3T magnetic resonance imaging. Both groups underwent 5 sets × 6 reps per session of squat separated by 3-min rest, while controlling the time under tension (within 0.5 and 0.8 s). RESULTS: The barbell squat group experienced moderate CSA increments in the VMMID and the VLDIST of the right leg (d=0.98-0.99). Additionally, the flywheel group experience large CSA increments in the RFMID, VLPROX and VLMID of the right leg (d=1.00-1.84). On average, flywheel squat training largely produced greater force during exercise compared to the barbell squat training (29.2 vs. 12.2 N·kg-1; d=5.95), whereas the barbell squat training produced moderately greater power output (10.5 vs. 9.7; d=0.52). CONCLUSIONS: Barbell squat training seems to be more effective for VM hypertrophy whereas flywheel squat triggers greater RF and VL hypertrophy as complementary to regular field-based soccer practice and competition within a short range of time (6 weeks) during the in-season. These findings can be considered also from either strength or reconditioning perspective based on the increase in the quadriceps muscles' CSA as mechanism underlying strength/power adaptations.