Biology subjects

Haralabidis, N.

Publications and source records attributed to Haralabidis, N..

3 recordsLinked to original sources

bioRxiv2025

Hamstrings muscle dynamics during the Nordic hamstring exercise and high-speed running

BackgroundThe Nordic hamstring exercise (NHE) and high-speed running are widely used training modalities to prevent hamstring strain injuries, yet the differences in the muscle lengths, forces, work, and power between these training modalities remain unclear. This study thus compared the dynamics of the most injured hamstrings muscle, biceps femoris long head (BFLH), for 14 participants (8 male and 6 female) performing the NHE and running between 4 and 8 m/s. MethodsWe used motion capture experiments and musculoskeletal simulation to quantify muscle fiber lengths and velocities, and muscle force, work, and power during the NHE and running. ResultsOur results show that peak muscle forces are greater during high-speed running (7.5 to 8 m/s) than the NHE, and that high-speed running also features longer muscle fiber lengths and higher muscle fiber lengthening velocities (p < 0.05). Negative muscle work was significantly greater during the NHE compared to running at all speeds (p < 0.001) because of the greater change in muscle fiber lengths during the NHE (p < 0.001). In contrast, peak negative muscle power was significantly lower during the NHE compared to running at 5 m/s and above (p < 0.01). ConclusionOur analysis reveals dramatic differences in the biomechanical demands of the NHE and running on the hamstrings muscles. Our results suggest that the two training modalities together provide complementary biomechanical stimuli to promote favorable BFLH injury prevention adaptations.

bioengineering↗

bioRxiv2025

Knee and Hip Joint Dynamics Differ between Sprinting and Nordic Hamstring Exercises

BackgroundSprinting and Nordic hamstring exercise (NHE) programs are common training modalities used to reduce hamstring injury risk, but the differences in the biomechanical demands of sprinting and the NHE are unclear. The purpose of this study was to compare knee and hip joint kinematics and kinetics, and hamstrings muscle-tendon unit (MTU) length and velocity during the flight phase of sprinting and the NHE. MethodsWe collected motion capture and force data from fourteen young athletic participants (8 males and 6 females) as they ran at a range of speeds (4-8 m/s) and performed the NHE. We used this experimental data and a musculoskeletal model to compute joint angles, moments, work, and power and to estimate the hamstrings MTU length and velocity for all running speeds and the NHE. ResultsThe peak knee flexion moment at running speeds of 6 m/s and above was greater than for the NHE (p < 0.001). Peak negative knee flexion power at all running speeds was higher than during the NHE (p < 0.001). Negative knee flexion work at running speeds of 6 m/s and slower was less than during the NHE (p < 0.001). Peak hamstrings length and lengthening velocity were greater (p < 0.001) for all running speeds compared to the NHE. ConclusionSprinting puts the hamstrings at longer hamstrings lengths and higher hamstrings lengthening velocities than the NHE. The NHE requires participants to generate peak knee flexion moments that are smaller than the peak knee flexion moments generated during top speed sprinting and peak negative knee flexion powers that are less than 5% of sprinting. However, the duration of each NHE repetition is approximately 60 times longer than the hamstrings lengthening portion of the flight phase of running, resulting in comparable negative knee work. The results of this study provide necessary quantitative information to compare the biomechanical demands of sprinting and the NHE.

bioengineering↗

bioRxiv2024

Simulations reveal how touchdown kinematic variables affect top sprinting speed: implications for coaching

Sprint performance is a priority for coaches and athletes. Several kinematic variables, including horizontal touchdown distance (HTD) and inter-knee touchdown distance (IKTD), are targeted by coaches to increase top sprinting speed. However, the results of past research are conflicting, potentially due to the use of experimental inter-athlete study designs where it is not possible to establish cause-effect relationships. In this study, we used a predictive simulation approach to assess cause-effect relationships between HTD and IKTD and sprinting speed. We scaled a three-dimensional musculoskeletal model to match the anthropometry of an international caliber male sprinter, and generated predictive simulations of a single symmetric step of top-speed sprinting using a direct collocation optimal control framework. We first used our simulation framework to establish the models top speed with minimal constraints on touchdown kinematics (the optimal simulation). Then, in additional simulations we enforced specific HTD or IKTD values ({+/-} 2, 4 and 6 cm compared to optimal). The model achieved a top speed of 11.85 m/s in the optimal simulation. Shortening HTD by 6 cm reduced speed by 7.3%, while lengthening HTD by 6 cm had a smaller impact on speed, with a 1.6% reduction. Speed in the simulation was insensitive to the IKTD changes we tested. The results of our simulations indicate there is an optimal HTD to maximize sprinting speed, providing support for coaches and athletes to adjust this technique variable. Conversely, our results do not provide evidence to support utilizing IKTD as a key technique variable for speed enhancement. We share the simulation framework so researchers can explore the effects of additional modifications on sprinting performance (https://github.com/nicos1993/Pred_Sim_Sprinting).

bioengineering↗