Statistical shape modelling reveals differences in hamstring morphology between professional rugby players and sprinters.

Hamstring morphology may play an important role in understanding the aetiology of hamstring injury. Currently, the methods available to capture detailed morphological data such as muscle shape have not been utilized for the hamstring muscles. The aim of this study was to examine the utility of statistical shape modelling (SSM) for describing and comparing hamstring muscle shape in rugby and sprinting athletes. Magnetic resonance images of both thighs of nine elite male rugby players and nine track and field sprinters were analysed. Images were converted to three-dimensional models enabling generation of four statistical shape models. Principal components describing the shape variation in the cohort were derived and evaluated. Six principal components were sufficient to discriminate differences in the shape of the hamstring muscles of rugby and sprinting athletes with 89% classification accuracy. Distinct shape features distinguishing rugby players from sprinters included size, curvature and axial torsion. These data demonstrate that SSM is useful for understanding hamstring muscle shape and that meaningful variation can be identified within a small sample. This method can be used in future research to enhance the anatomical specificity of musculoskeletal modelling and to understand the relationship between hamstring shape and injury.

Hamstring musculotendon mechanics of prospectively injured elite rugby athletes.

The musculotendon mechanics of the hamstrings during high-speed running are thought to relate to injury but have rarely been examined in the context of prospectively occurring injury. This prospective study describes the hamstring musculotendon mechanics of two elite rugby players who sustained hamstring injuries during on-field running. Athletes undertook biomechanical analyses of high-speed running during a Super Rugby pre-season, prior to sustaining hamstring injuries during the subsequent competition season. The biceps femoris long head muscle experienced the greatest strain of all hamstring muscles during the late swing phase. When expressed relative to force capacity, biceps femoris long head also experienced the greatest musculotendon forces of all hamstring muscles. Musculotendon strain and force may both be key mechanisms for hamstring injury during the late swing phase of running.

The effect of footwear on mechanical behaviour of the human ankle plantar-flexors in forefoot runners.

PURPOSE: To compare the ankle plantar-flexor muscle-tendon mechanical behaviour during barefoot and shod forefoot running. METHODS: Thirteen highly trained forefoot runners performed five overground steady-state running trials (4.5 ± 0.5 m.s-1) while barefoot and shod. Three-dimensional kinematic and ground reaction force data were collected and used as inputs for musculoskeletal modelling. Muscle-tendon behaviour of the ankle plantar-flexors (soleus; medial gastrocnemius; and lateral gastrocnemius) were estimated across the stance phase and compared between barefoot and shod running using a two-way multivariate analysis of variance. RESULTS: During barefoot running peak muscle-tendon unit (MTU) power generation was 16.5% (p = 0.01) higher compared to shod running. Total positive MTU work was 18.5% (p = 0.002) higher during barefoot running compared to shod running. The total sum of tendon elastic strain energy was 8% (p = 0.036) greater during barefoot compared to shod running, however the relative contribution of tendon and muscle fibres to muscle-tendon unit positive work was not different between conditions. CONCLUSION: Barefoot forefoot running demands greater muscle and tendon work than shod forefoot running, but the relative contribution of tendon strain energy to overall muscle-tendon unit work was not greater.

A retrospective analysis of hamstring injuries in elite rugby athletes: More severe injuries are likely to occur at the distal myofascial junction.

OBJECTIVES: To describe the most common hamstring injury scenarios and outcomes in elite rugby union. DESIGN: Retrospective investigation. SETTING: Hamstring injury data from an elite rugby union team was collected over five seasons and retrospectively analysed. PARTICIPANTS: 74 professional rugby players. MAIN OUTCOME MEASURES: Injuries were classified as new or recurrent. Injury severity, activity, player position, and whether the injury occurred during a match or training was determined for each injury. Injury location and grade were determined for more clinically severe injuries where Magnetic Resonance Imaging (MRI) data was available (15 injuries). RESULTS: Thirty hamstring injuries were sustained over the five seasons. The majority of injuries were new (93%), moderate in severity (60%) and occurred during running (77%). For more clinically severe injuries, the biceps femoris long head (BFlh) was the most commonly injured muscle (73%) and the distal myofascial junction (DMFJ) was the most common injury site (58% of BFlh injuries). CONCLUSIONS: Hamstring injuries most commonly occurred while running and in the BFlh muscle, which is similar to other sports. However, the most common intramuscular injury site was the DMFJ, which contrasts with reports from other cohorts. Future studies should ensure to include the myofascial junction when classifying injury location.

Late swing running mechanics influence hamstring injury susceptibility in elite rugby athletes: A prospective exploratory analysis.

Hamstring injuries are one of the most prevalent injuries in rugby union and many other running-based sports, such as track sprinting and soccer. The majority of these injuries occur during running; however, the relationship between running mechanics and hamstring injury is unclear. Obtaining large samples of prospective injury data to examine this relationship is difficult, and therefore exploratory analysis frameworks may assist in deriving valuable information from studies with small but novel samples. The aim of this study was to undertake a prospective exploratory analysis of the relationship between running mechanics and hamstring injury. Kinematic and kinetic data of the trunk, pelvis and lower limbs were collected during maximal overground running efforts for ten elite rugby union athletes. Subsequently, hamstring injury occurrence was recorded for the following Super Rugby season, during which three athletes sustained a running-based hamstring injury. Functional principal component analysis was used to visualise patterns of variability in running mechanics during the late swing phase between athletes. Results indicated that subsequently injured athletes demonstrated a tendency for greater thoracic lateral flexion, greater hip extension moments and greater knee power absorption, compared to uninjured athletes. All variables demonstrated an ability to descriptively differentiate between injured and uninjured athletes at approximately 60% of the late swing phase. Therefore, we hypothesize that greater thoracic lateral flexion, a greater hip extension moment and greater knee power absorption between peak hip flexion and peak knee extension during the late swing phase may put rugby athletes at greater risk of running-based hamstring injury.

Late swing or early stance? A narrative review of hamstring injury mechanisms during high-speed running.

Hamstring injuries are highly prevalent in many running-based sports, and predominantly affect the long head of biceps femoris. Re-injury rates are also high and together lead to considerable time lost from sport. However, the mechanisms for hamstring injury during high-speed running are still not fully understood. Therefore, the aim of this review was to summarize the current literature describing hamstring musculotendon mechanics and electromyography activity during high-speed running, and how they may relate to injury risk. The large eccentric contraction, characterized by peak musculotendon strain and negative work during late swing phase is widely suggested to be potentially injurious. However, it is also argued that high hamstring loads resulting from large joint torques and ground reaction forces during early stance may cause injury. While direct evidence is still lacking, the majority of the literature suggests that the most likely timing of injury is the late swing phase. Future research should aim to prospectively examine the relationship between hamstring musculotendon dynamics and hamstring injury.

Effects of Altering Trunk Position during Landings on Patellar Tendon Force and Pain.

PURPOSE: This study aimed to verify the immediate effects of altering sagittal plane trunk position during jump landings on lower limb biomechanics, patellar tendon force, and pain of athletes with and without patellar tendinopathy. METHODS: Twenty-one elite male athletes were categorized into three groups: athletes with patellar tendinopathy (TG; n = 7), asymptomatic athletes with patellar tendon abnormalities (n = 7), and asymptomatic athletes without tendon abnormalities (CG; n = 7). A biomechanical evaluation was conducted while the athletes performed drop landings from a bench in a self-selected trunk position (SS). Afterward, the athletes were randomly assigned to land with either a flexed trunk position (FLX) or an extended trunk position (EXT). Variables of interest for this study included sagittal plane peak kinematics, kinetics, patellar tendon force, and pain during the landing tasks. RESULTS: Peak patellar tendon force, knee extensor moment, and knee pain decreased in the FLX landing compared with the SS landing, regardless of group. In addition, peak patellar tendon force, knee extensor moment, and vertical ground reaction force were smaller in the FLX landing compared with the EXT landing. The TG had smaller peak ankle dorsiflexion compared with the CG during jump landings, regardless of trunk position. CONCLUSIONS: Landing with greater trunk flexion decreased patellar tendon force in elite jumping athletes. An immediate decrease in knee pain was also observed in symptomatic athletes with a more flexed trunk position during landing. Increasing trunk flexion during landing might be an important strategy to reduce tendon overload in jumping athletes.

A simple method for quantifying jump loads in volleyball athletes.

OBJECTIVES: Evaluate the validity of a commercially available wearable device, the Vert, for measuring vertical displacement and jump count in volleyball athletes. Propose a potential method of quantifying external load during training and match play within this population. DESIGN: Validation study. METHODS: The ability of the Vert device to measure vertical displacement in male, junior elite volleyball athletes was assessed against reference standard laboratory motion analysis. The ability of the Vert device to count jumps during training and match-play was assessed via comparison with retrospective video analysis to determine precision and recall. A method of quantifying external load, known as the load index (LdIx) algorithm was proposed using the product of the jump count and average kinetic energy. RESULTS: Correlation between two separate Vert devices and three-dimensional trajectory data were good to excellent for all jump types performed (r=0.83-0.97), with a mean bias of between 3.57-4.28cm. When matched against jumps identified through video analysis, the Vert demonstrated excellent precision (0.995-1.000) evidenced by a low number of false positives. The number of false negatives identified with the Vert was higher resulting in lower recall values (0.814-0.930). CONCLUSIONS: The Vert is a commercially available tool that has potential for measuring vertical displacement and jump count in elite junior volleyball athletes without the need for time-consuming analysis and bespoke software. Subsequently, allowing the collected data to better quantify load using the proposed algorithm (LdIx).