Swing Phase Mechanics of Maximal Velocity Sprints-Does Isokinetic Lower-Limb Muscle Strength Matter?

PURPOSE: Concentric hip and eccentric knee joint mechanics affect sprint performance. Although the biarticular hamstrings combine these capacities, empirical links between swing phase mechanics and corresponding isokinetic outcome parameters are deficient. This explorative study aimed (1) to explain the variance of sprint velocity, (2) to compare maximal sprints with isokinetic tests, (3) to associate swing phase mechanics with isokinetic parameters, and (4) to quantify the relation between knee and hip joint swing phase mechanics. METHODS: A total of 22 sprinters (age = 22 y, height = 1.81 m, weight = 77 kg) performed sprints and eccentric knee flexor and concentric knee extensor tests. All exercises were captured by 10 (sprints) and 4 (isokinetics) cameras. Lower-limb muscle balance was assessed by the dynamic control ratio at the equilibrium point. RESULTS: The sprint velocity (9.79 [0.49] m/s) was best predicted by the maximal knee extension velocity, hip mean power (both swing phase parameters), and isokinetic peak moment of concentric quadriceps exercise (R2 = 60%). The moment of the dynamic control ratio at the equilibrium point (R2 = 39%) was the isokinetic parameter with the highest predictive power itself. Knee and hip joint mechanics affected each other during sprinting. They were significantly associated with isokinetic parameters of eccentric hamstring tests, as well as moments and angles of the dynamic control ratio at the equilibrium point, but restrictedly with concentric quadriceps exercise. The maximal sprints imposed considerably higher loads than isokinetic tests (eg, 13-fold eccentric knee joint peak power). CONCLUSIONS: Fast sprinters demonstrated distinctive knee and hip mechanics in the late swing phase, as well as strong eccentric hamstrings, with a clear association to the musculoarticular requirements of the swing phase in sprinting. The transferability of isokinetic knee strength data to sprinting is limited inter alia due to different hip joint configurations. However, isokinetic tests quantify specific sprint-related muscular prerequisites and constitute a useful diagnostic tool due to their predicting value to sprint performance.

Nordic Hamstring Exercise training induces improved lower-limb swing phase mechanics and sustained strength preservation in sprinters.

Nordic Hamstring Exercise (NHE) training improves eccentric hamstring strength and sprint performance. However, detraining causes rapid reductions of achieved adaptations. Furthermore, the transfer of improved hamstring capacity to swing phase mechanics of sprints is unknown. This longitudinal study aimed (a) to quantify NHE-induced adaptations by camera-based isokinetic assessments and sprint analyses, (b) to relate the magnitude of adaptations to the participants' initial performance level, (c) to investigate the transferability to sprints, and (4) to determine strength preservations after 3 months. Twelve sprinters (21 years, 1.81 m, 74 kg) were analyzed throughout 22 weeks. They performed maximal sprints and eccentric knee flexor and concentric knee extensor tests before and after a 4-week NHE training. Sprints and isokinetic tests were captured by ten and four high-speed cameras. The dynamic control ratio at the equilibrium point (DCRe) evaluated thigh muscle balance. High-intensity NHE training elicited significant improvements of hamstring function (P range: <.001-.011, d range: 0.44-1.14), thigh muscle balance (P < 0.001, d range: 0.80-1.08) and hamstring-related parameters of swing phase mechanics (P range: <0.001-0.022, d range: 0.12-0.57). Sprint velocity demonstrated small increases (+1.4%, P < 0.001, d = 0.26). Adaptations of hamstring function and thigh muscle balance revealed moderate to strong transfers to improved sprint mechanics (P range: <0.001-0.048, R2 range: 34%-83%). The weakest participants demonstrated the highest adaptations of isokinetic parameters (P range: 0.003-0.023, R2 range: 42%-62%), whereas sprint mechanics showed no effect of initial performance level. Three months after the intervention, hamstring function (+6% to +14%) and thigh muscle balance (+8% to +10%) remained significantly enhanced (P < 0.001, ƞp 2 range: 0.529-0.621). High-intensity NHE training induced sustained improved hamstring function of sprinters, which can be transferred to swing phase mechanics of maximal sprints. The initial performance level, NHE training procedures and periodization should be considered to optimize adaptations.

Effect of an ankle-foot orthosis on knee joint mechanics: a novel conservative treatment for knee osteoarthritis.

BACKGROUND: Several conservative treatments for medial knee osteoarthritis such as knee orthosis and laterally wedged insoles have been shown to reduce the load in the medial knee compartment. However, those treatments also present limitations such as patient compliance and inconsistent results regarding the treatment success. OBJECTIVE: To analyze the effect of an ankle-foot orthosis on the knee adduction moment and knee joint alignment in the frontal plane in subjects with knee varus alignment. STUDY DESIGN: Controlled laboratory study, repeated measurements. METHODS: In total, 14 healthy subjects with knee varus alignment were analyzed in five different conditions: without orthotic, with laterally wedged insoles, and with an ankle-foot orthosis in three different adjustments. Three-dimensional kinetic and kinematic data were collected during gait analysis. RESULTS: Significant decreases in knee adduction moment, knee lever arm, and joint alignment in the frontal plane were observed with the ankle-foot orthosis in all three different adjustments. No significant differences could be found in any parameter while using the laterally wedged insoles. CONCLUSION: The ankle-foot orthosis was effective in reducing the knee adduction moment. The decreases in this parameter seem to be achieved by changing the knee joint alignment and thereby reducing the knee lever arm in the frontal plane. CLINICAL RELEVANCE: This study presents a novel approach for reducing the load in the medial knee compartment, which could be developed as a new treatment option for patients with medial knee osteoarthritis.

Kinetics of cross-slope running.

The purpose of the present study was to identify kinetic responses to running on mediolaterally elevated (cross-sloped) running surfaces. Ground reaction forces (GRFs), GRF lever arms and joint moment characteristics of 19 male runners were analyzed when running at 3.5m/s on a custom-made, tiltable runway. Tilt angles of 3° and 6° for medial and lateral elevation were analyzed using a 10 camera Vicon Nexus system and a force platform. The point of force application of the GRF showed a systematic shift in the order of 1-1.5cm to either the lateral or medial aspect of the foot for lateral or medial inclinations, respectively. Consequently, the strongest significant effects of tilt orientation and level on joint kinetics and ground reaction force lever arms were identified at the ankle, knee and hip joint in the frontal plane of movement. External eversion moments at the ankle were significantly increased by 35% for 6° of lateral elevation and decreased by 16% for 6° of medial elevation. Altering the cross-slope of the running surface changed the pattern of ankle joint moments in the transversal plane. Effect sizes were on average larger for laterally elevated conditions, indicating a higher sensitivity of kinetic parameters to this kind of surface tilt. These alterations in joint kinetics should be considered in the choice of the running environment, especially for specific risk groups, like runners in rehabilitation processes.