ECSS Paris 2023: OP-BM04
INTRODUCTION: High-intensity displacement (HID) has been characterized through high-velocity running and intense acceleration, analyzed independently. This does not account for the interplay between acceleration and running velocity and has been identified as a drawback since maximal acceleration capacity decreases continuously with velocity. Recently, HID relative threshold has been defined over the velocity spectrum as a fraction of maximal capacities considering running velocity effects on either maximal acceleration (acceleration-speed relationship: %AS) or external power output (%Pext-V). Considering both external and internal power (%Ptot-V) has not been tested yet. The aim was to compare the amount and distribution along the entire velocity continuum (from null to maximal running velocity S0) of HID detected by traditional method (TRAD, fraction of maximal acceleration and velocity) with recent %AS, %Pext-V and %Ptot-V methods. METHODS: 61 youth rugby union players (29 backs, 32 forwards from U18 and U21 French Division 1) were enrolled. Maximal capacities according to each method (maximal acceleration and velocity, and AS, Pext-V, Ptot-V relationships) were determined from all season training sessions and games. Average game events above HID threshold were detected for each method as 75% of maximal capacities, and corresponding high-intensity work (HIW) was calculated. Correlations in HIW between methods were tested at both team and position (forwards vs. backs) levels. Distribution and magnitude of HIW along the velocity axis (%S0) were analyzed continuously with kernel density estimation. Between-method density curves were compared with statistical parametric mapping (SPM). RESULTS: At team level, TRAD displays high to very high correlation with %AS (r=0.84), %Pext-V (r=0.89), %Ptot-V (r=0.91). Correlations were slightly altered at position level with r ranging 0.80-0.88 for forwards and 0.82-0.87 for backs, associated with differences in HIW up to 207% between methods for a player. %AS showed very high correlation at both team and position level with %Pext-V (r=0.97) and %Ptot-V (r=0.97). %Pext-V and %Ptot-V showed nearly perfect correlation at any level (r=1.00). SPM analysis revealed that TRAD detected more HIW than %AS, %Pext-V and %Ptot-V at approximately 65-90% S0, whereas the opposite was observed at 20-50% S0. Moreover, %Pext-V and %Ptot-V detected more HIW than %AS at 2-92% S0, and %Ptot-V detected more HIW than %Pext-V at 8-95% S0. CONCLUSION: Even if TRAD correlates with recent %AS, %Pext-V and %Ptot-V methods, distribution of HID is shifted toward moderate to high velocities, potentially including low acceleration and high velocity events far from maximal capacity. TRAD could thus be limited in homogeneous populations or acceleration-oriented activity analysis. Recent methods are very highly correlated, with differences in HID being homogeneously distributed throughout the velocity spectrum but important differences in total HIW detected, %AS being the most restrictive.
Read CV Tommy GrangeECSS Paris 2023: OP-BM04
INTRODUCTION: The ability to rapidly increase muscle force (explosiveness) and dynamic force production capacities across different velocities (force-velocity-power capacities) are known to be two different determinants of ballistic contractions. However, when the force-velocity relationship is obtained from averaged values over a dynamic contraction, these two determinants may interact. Indeed, at any given time of the contraction, the maximal force the neuromuscular system can produce depends on the muscle shortening velocity and length, and the time from the initiation of the contraction. Recently, Boccia et al. (2025) showed that explosiveness (Rate of Torque Development, RTD) was correlated to maximal velocity (V0) and power (Pmax), but not maximal torque (T0), during isoinertial knee extensions. However, the understanding of this interaction may have been limited by interindividual variability in force-velocity, -length and -time relationships. The aim was to clarify the sensitivity of T0, V0 and Pmax to change in RFD from simulations of a simple model of knee extension. METHODS: Considering intrinsic hyperbolic torque-velocity, polynomial torque-length and exponential torque-time relationships, forward simulations of the knee extensors’ (KE) external torque were conducted over time during maximal dynamic knee extensions against various loads. External Torque (T)-Velocity (V) relationships of KE were obtained from fitting averaged values (100-130° knee angle) of T and V using a Hill-type function to derive external T0, V0 and Pmax. The sensitivity of T0, V0 and Pmax to change in RTD was i) tested via simulations of external TV relationship using time constant of the force-time curve from 0.05 to 0.15s, ceteris paribus, and ii) quantified from various T0 (150 to 350 N.m) and V0 (600 to 1400°/s) values. RESULTS: For typical values of T0 (250 N.m) and V0 (1000°/s), a 100% change in RTD (usually observed within population) affect positively V0 (+10.4%) and Pmax (+19.4%), and negatively T0 (-5.3%). When T0 changes from 150 to 350 N.m, the sensitivities of T0, V0 and Pmax to change in RTD remain quite unchanged. In contrast, when V0 changes from 600 to 1400°/s, the sensitivities of V0 and Pmax to change in RTD increase from 3.1 to 15.3% and from 14.2 to 23.3%, respectively, while no main change observed for T0. CONCLUSION: During dynamic contractions, the explosiveness interacts with muscle intrinsic TV and force-length relationships, resulting in differences between intrinsic and external TV relationships. The latter, when obtained from contraction-averaged values, is thus affected by RTD, with a substantial positive sensitivity for V0 and Pmax: the lower RTD, the lower external V0 or Pmax for the same intrinsic muscle capacities. This sensitivity is higher for high V0 values, supporting that a decrease in RTD alters more V0 if V0 is high, due to the quickness of the contraction. Boccia et al, SJMSS 2025 Mar;35(3)
Read CV Pierre SamozinoECSS Paris 2023: OP-BM04
INTRODUCTION: In vitro evidence indicates an effect of female sex hormones (i.e., estrogen and progesterone) on the microstructure of collagenic tissues [1,2]. However, if and how these changes translate into mechanical alterations in muscles and/or tendons in vivo remains debated. The current study aimed to investigate the effects of hormone levels on the mechanical properties of lower leg muscle-tendon units during maximal voluntary contractions (MVCs) and explosive isometric contractions. METHODS: Thirty-three active healthy women (age: 24.1 ± 2.7 years) were recruited and assigned to two groups based on oral contraceptive (OC) use: non-users (NOC; n= 18) or users (OC; n= 15, all on combined monophasic pills). The experimental session involved: blood sample collection for hormones concentration analysis, followed by strength measurements of the dominant leg to determine maximal isometric torque and rate of torque development during knee extensions and flexions, and ankle plantar- and dorsi-flexions. The mechanical behaviour of vastus lateralis, gastrocnemius medialis, tibialis anterior, Achilles (AT) and patellar (PT) tendon were investigated with ultrasound apparatuses. NOC group repeated the session in two menstrual cycle phases (follicular and luteal), while the OC group was tested only once. RESULTS: There were no significant differences between menstrual cycle phases and between NOC and OC groups in terms of maximal isometric torque, maximal AT or PT elongation, and belly shortening of the investigated muscles. Neither menstrual cycle phases nor contraceptive use had an effect on patellar tendon stiffness, but the Achilles tendon stiffness was reduced during the luteal phase compared to the follicular one at high torque levels (INTENSITY*PHASE p= 0.065). The stiffness of the three investigated muscles did not differ between cycle phases or groups. OC use impacted the knee extension rate of torque development, with higher values observed in OC users compared to both menstrual cycle phases (follicular, p= 0.002; luteal, p= 0.035). CONCLUSION: Hormonal fluctuations across the menstrual cycle only slightly affect Achilles (but not patellar) tendon behaviour, with no measurable effects on mechanical output. Oral contraceptive use did not alter the mechanical properties of the lower limb muscle-tendon structures during maximal contractions, but had a favorable impact on the explosive strength of knee extensors. References [1] Leblanc et al., The Journal of Steroid Biochemistry and Molecular Biology (2017) [2] Lee et al., Journal of Applied Physiology (2015)
Read CV Davide LatiniECSS Paris 2023: OP-BM04