Relationship between vastus lateralis muscle ultrasound echography, knee extensors rate of torque development, and jump height in professional soccer athletes

Acute Effects of Intracontrast Rest After Back Squats on Vertical Jump Performance During Complex Training

ABSTRACT

Houlton, LJ, Moody, JA, Bampouras, TM, and Esformes, JI. Acute effects of intracomplex rest after back squats on vertical jump performance during complex training. J Strength Cond Res XX(X): 000-000, 2024-Postactivation performance enhancement and complex-contrast sets are prevalent in sports science research. Typical complex-contrast sets consist of heavy back squats, an intracontrast rest period (ICRP) and vertical jumps (countermovement jumps [CMJs], or squat jumps [SJs]). Propulsive impulse (Jprop) is considered the leading indicator of jump performance. However, studies evaluating jump performance during complex-contrast sets use jump height as the primary performance measure, limiting insight into ICRP's effect on jump performance. We assessed the effect of a 3 repetition maximum (3RM) back squat and 6 ICRPs on vertical jump Jprop and associated force-time components. Fourteen subjects completed 12 experimental conditions, assigned equally to 4 testing sessions. Independent variables, in a 6 × 2 randomized, counterbalanced design, were ICRP (0, 60, 120, 180, 240, 300 seconds; ICRP0, ICRP60, ICRP120, ICRP180, ICRP240, ICRP300, respectively) and vertical jump (CMJ and SJ). Conditions consisted of baseline vertical jumps, followed by 3 back squat repetitions at 100% 3RM, an ICRP and experimental jumps. Symmetrized percentage changes between experimental and baseline jumps were assessed using repeated measures analysis of variance (ANOVA) and pairwise effect sizes. Results showed significant effects (p ≤ 0.05) on CMJ average rate of force development (RFD) between ICRP0 and ICRP120 and ICRP0 and ICRP300. Pairwise comparisons showed medium and large effect sizes for and increases in CMJ RFD (g = 0.83-2.69) whereas SJ RFD decreased (g = 0.81-2.57). Small effect sizes were found for Jprop, peak force, and mean force. Results suggest limited change in Jprop (g = 0.01-0.58), but back squats may potentiate RFD via the stretch-shortening cycle.

Maximal vs. explosive knee extensor strength in professional soccer players: inter-limb asymmetries and relationship with knee function

AbstractThe main aims of this study were to compare the magnitude of inter-limb asymmetry (ILA) and the relation with self-reported knee function between maximal and explosive knee extensor strength outcomes in professional soccer players. Forty-six male soccer players completed different maximal isokinetic and isometric contractions of the knee extensors for the assessment of maximal strength (peak torque and maximal voluntary contraction (MVC) torque) and explosive strength (early, intermediate, late, and peak rate of torque development (RTD)). Self-reported knee function was assessed with the International Knee Documentation Committee (IKDC) and Lysholm knee scoring scales. Peak torque and MVC torque showed comparable ILAs (8-9%), both being significantly lower than all RTD ILAs (16% on average; p < 0.001). ILAs for early RTD (21%) and peak RTD (19%) were significantly higher than all the other variables (p < 0.05). Only early and intermediate RTD were significantly correlated - though weakly - with both IKDC (rho = 0.32 for both) and Lysholm (rho = 0.36 and 0.30, respectively) scores. We conclude that explosive knee extensor strength - early RTD in particular - exhibited larger ILAs and better relations with self-reported knee function than peak torque and MVC torque in professional soccer players. These results confirm the validity and functional relevance of early RTD and the need for its inclusion in routine performance testing for soccer players.

Faster intrinsic rate of torque development in elbow flexors than knee extensors: Effect of muscle architecture?

We studied the effect of pennate vs. fusiform muscle architecture on the rate of torque development (RTD) by examining the predominately fusiform elbow flexors (EF) and highly-pennate knee extensors (KE). Seventeen male volunteers (28.4 ± 6.2 years) performed explosive isometric EF and KE contractions (MVCs). Biceps brachii and vastus lateralis fascicle angles were measured to confirm their architecture, and both the rate of voluntary muscle activation (root-mean-square EMG in the 50 ms before contraction onset; EMG_-50) and electromechanical delay (EMD; depicting muscle-tendon series elasticity) were assessed as control variables to account for their influence on RTD. MVC torque, early (RTD₅₀) and late (RTD₂₀₀) RTDs were calculated and expressed as absolute and normalized values. Absolute MVC torque (+412%), RTD₅₀ (+215%), and RTD₂₀₀ (+427%) were significantly (p < 0.001) higher in KE than EF. However, EF RTD₅₀ was faster (+178%) than KE after normalization (p = 0.02). EMG_-50 and EMD did not differ between muscle groups. The results suggest that the faster absolute RTD in KE is largely associated with its higher maximal torque capacity, however in the absence of differences in rates of muscle activation, fiber type, and EMD the fusiform architecture of EF may be considered a factor allowing its faster early RTD relative to strength capacity.

Relationship between upper and lower limbs muscle explosive strength with the vastus lateralis and biceps brachii architecture

ABSTRACT We aimed to assess upper and lower limbs explosive strength, and its correlation with biceps brachii (BB) and vastus lateralis (VL) architecture. Absolute and maximum torque normalized rate of torque development (RTD) were measured from isometric elbow flexion (EF) and knee extension (KE). BB and VL architectures were assessed by ultrasound. Absolute RTD of KE was higher (129–272%), although normalized RTD was higher in EF (80-21%). The absolute RTD was correlated to muscle thickness only in the BB (r=.39-46). No relationship was found between muscle architecture and normalized RTD. In conclusion, the higher RTD from KE seems to be due to their greater strength. Only the muscle architecture could not explain the differences found in the RTD.