ECSS Paris 2023: OP-MH13
INTRODUCTION: Recent research suggests that return-to-play protocols may benefit from the inclusion of angle-specific hamstring:quadriceps (H:Q) ratios to accurately understand muscle balance through the ROM (Lunn et al. 2023). In undertaking angle-specific analyses, most isokinetic knee extension-flexion protocols are conducted using concurrent repetitions (CON) whereby active knee extension is immediately followed by active knee flexion. To reduce the influence of the stretch-shortening cycle and limit axis misalignment, isolated repetitions (ISO) have been recommended (Alt et al. 2014) whereby extension and flexion are completed separately. To inform athlete screening protocols, this study examined the effect of CON and ISO protocols on discrete and angle-specific hamstring:quadriceps ratios. METHODS: Fifteen healthy males (age: 27 ± 4 years; height: 184 ± 9 cm; body mass: 80 ± 9 kg) performed isokinetic tests of the knee flexors and extensors (60 deg/s) using CON and ISO repetitions while sagittal-plane kinematics were captured (100 Hz) to quantify axis misalignment. Statistical parametric mapping then enabled the effects of protocol type (CON vs. ISO) and axis misalignment (uncorrected vs. corrected data) to be compared. RESULTS: The use of uncorrected data resulted in an underestimation of discrete conventional (−10.2%, p < 0.001) and functional (−9.2%, p < 0.05) H:Q ratios with these differences being observed for all angle-specific ratios (p < 0.001). The use of concurrent repetitions resulted in a significant overestimation of the H:Q ratio (+7.4%, p < 0.05) with the differences being most prevalent at extended knee joint positions. Despite the main effect(s) of protocol type and axis misalignment, no significant interactions were observed. CONCLUSION: Practitioners should be mindful that the use of concurrent repetitions will result in a significantly higher conventional H:Q ratio which will particularly influence angle-specific ratios in more extended knee joint positions. This may increase the likelihood of “false negative” injury risk categorisation during “time-efficient” protocols involving concurrent repetitions. Whilst the use of corrected knee moment data is preferable, practitioners should be mindful that the use of isolated repetitions and corrected joint moment data does not lead to significant differences in discrete or angle-specific H:Q ratios when compared with uncorrected data obtained from concurrent repetitions. References Alt, T. et al., (2014) Isokinetics and Exercise Science, 22, pp.333–342 Lunn, DE, et al., (2023) Journal of Strength & Conditioning Research, 10, pp.1519
Read CV Gareth NicholsonECSS Paris 2023: OP-MH13
INTRODUCTION: Genu varum has been shown to be particularly prevalent in soccer players and to increase over time. Several causes have been suggested for genu varum in soccer, including muscular asymmetry and imbalanced overloading of the growth plates. Studies have also shown that this process already begins in childhood and adolescence. The development and increase of genu varum lead to biomechanical changes, increases the risk of osteoarthritis and causes tension shifts within the ligaments. This exploratory study aims to provide insight into the relationship between genu varum and athletic performance in elite youth soccer players. METHODS: In this study, 247 healthy male soccer players in the Under-12 to Under-18 squads (age 14.64 ± 2.13 years (mean ± standard deviation); body weight: 56.82 ± 14.42 kg, standing body height: 168.19 ± 13.2 cm, years of playing soccer: 9.07 ± 2.76 years, skeletal muscle mass: 28.53 ±7.94 kg) from two German elite youth academies were investigated in August 2023. Performance tests included the 30m linear sprint, the counter movement jump (CMJ), and the heading jump. The intercondylar distance (ICD) was measured using a digital caliper in cm. A linear regression was performed between the ICD and the performance parameters sprint speed (30m linear sprint) and CMJ or heading jump height. An alpha level of .05 (2-tailed) was considered significant. RESULTS: The overall mean ICD was 1.92 ± 1.8 cm. Regression analysis revealed significant relationships for sprint speed (beta = -0.46, p ≤ .001), CMJ jump height (beta = 0.53, p ≤ .001), and for heading jump height (beta = 0.41, p ≤ .001). Significant relationships were also found for sprint speed (beta = -0.14, p ≤ .001), CMJ jump height (beta = 0.18, p ≤ .001), and for heading jump height (beta = 0.09, p ≤ .04), when the model was adjusted for the athlete’s skeletal muscle mass. CONCLUSION: Our study provides evidence that genu varum is associated with an increase in sprint and jump performance in elite male youth soccer players. Future research is warranted in female athletes and in other team sports with similar physical demands.
Read CV Alexander-Stephan HenzeECSS Paris 2023: OP-MH13
INTRODUCTION: Why do athletes injure themselves without external contact, why do they develop musculoskeletal complaints, often only on one side despite similar load on both sides? Mechanisms of injuries and musculoskeletal complaints have not yet been satisfactorily decoded. Research has mainly focused on muscle strengths but has not provided a plausible explanation for the underlying mechanisms. We postulate that it is not muscle strength but stability that should be the focus in order to decipher the enigma. The neuromuscular system has to stabilize joints in reaction to external forces in daily life or sports. Assessments of muscle function should include this aspect. This actually depends on the capacity of adapting to external loads. We collected data for a still unconsidered muscle function, termed Adaptive Force (AF). The aim was to characterize stable vs. unstable muscles. METHODS: The max. holding function (AFisomax) is assessed by adapting to an increasing external load during holding isometric muscle action. Data of 6 studies (n=72 participants, elbow/hip flexors) were analyzed regarding the max. AF, AFisomax and AF at onset of muscle oscillations (AFosc). An objectified manual muscle test was rated as stable (486 trials) or unstable (308 trials) by the tester regarding the participant’s capacity to maintain the static starting position until high forces (stable) or to merge into muscle lengthening at submaximal intensities (unstable), respectively. The arithmetic mean of AF parameters of all stable or unstable trials per muscle and participant was calculated and used for statistics to characterized muscle stability and instability. RESULTS: The maxAF did not differ significantly between unstable vs. stable (p=0.240), but the AFisomax was significantly lower (p<0.001) and AFosc significantly higher (p<0.001). The ratio AFisomax/maxAF amounted ~99.4±1.8% for stable and ~55.8±16% for unstable muscles (p<0.001). Oscillations occurred during isometric action for stable muscles; for unstable muscles they emerged if at all in the lengthening phase (p<0.001). The ratios did not depend on the testers or muscles assessed, although maxAF, AFisomax and AFosc were lower for the female vs. male tester. The included Long COVID study and case examples indicate that in post-infectious states, stress and joint pain the AFisomax, but not maxAF is reduced and stabilizes after recovery. CONCLUSION: Muscle instability can be characterized by a low holding capacity, but not by a reduced max force. Muscle oscillations arise during stability and may be a sign and prerequisite for it. The studies indicate that the holding capacity is more sensitive to disruptive but also supportive stimuli. These findings could close the gap of the still unsolved mechanisms of injuries or musculoskeletal complaints. The evidence is high to claim to shift the focus from strength to stability in research and clinical practice. Applied research to verify this hypothesis is urgently needed.
Read CV Frank BittmannECSS Paris 2023: OP-MH13