LEE, MARCUS J. C.; REID, SIOBHAN L.; ELLIOTT, BRUCE C.; LLOYD, DAVID G.

Following an intial hamstring injury, re-injury is a common problem. The functional reasons for this remain unclear. This study looks at differences in swing phase running biomechanics and isokinetic strength, between the previously hamstring-injured and uninjured limbs of male athletes involved in sprint-based sports.

Athletes, underwent 3D motion analysis to determine bilateral joint kinematics and kinetics during submaximal sprinting. Various hip and knee isokinetic strength tests were performed bilaterally using a Biodex dynamometer. Peak torque (PT) and total work (TW; normalized to body mass) were collected isokinetically from concentric hamstrings (CH), concentric quadriceps (CQ), concentric hip flexors (CHF), and eccentric hamstrings (EH). Three PT and TW ratios were created, namely, CH/CQ, EH/CQ, and EH/CHF, and were compared between the previously injured and uninjured limbs.

The results show that lower limb swing phase kinematics and kinetics were similar. Only peak hip flexion angle in late swing was significantly reduced (1.9[degrees]) in the previously injured limb. EH PT was decreased and occurred at shorter hamstring lengths on the previously injured side, whereas CQ TW was increased by 13.6 Jkg-1. EH/CQ and EH/CHF ratios for PT and TW were reduced on the previously injured limbs.

The rearch concluded that although swing phase biomechanics of submaximal sprinting were similar between limbs, the previously injured hamstrings did display significant weakness eccentrically. Residual eccentric weakness may predispose this muscle group to reinjury during late swing, compared with the uninjured limb, because the functional eccentric demand on both limbs was similar. Furthermore, the EH/CHF ratios may better reflect muscle function during sprinting, having the potential to influence rehabilitation to prevent reinjury.

Medicine & Science in Sports & Exercise. 41(10):1942-1951, October 2009.

P W Kong, N G Candelaria, D R Smith  

In this study, the effect of shoe degradation on running biomechanics by comparing the kinetics and kinematics of running in new and worn shoes was investigated. Three types of footwear using different cushioning technologies were compared.

24 runners (14 male and 10 female) were tested Pre and post 200 miles of road running in the smae pair of shoes. The runners were given either air/gel/spring cushioned trainers. Testing consisted of overground running at 4.5 m s^–1 on a 20-m laboratory runway; performance measured using a force platform and a motion capture system.

Stance time was calculated from force data. External loads were measured by maximum vertical force and loading rate. Kinematic changes were indicated by sagittal plane angles of the torso, hip, knee and ankle at critical events during the stance phase.

Results demonstrated that stance time increases in worn shoes. The torso displayed less maximum forward lean and less forward lean at toe-off , while the ankle displayed reduced maximum dorsiflexion and increased plantar flexion at toe-off  in worn shoes. No changes in the hip and knee angles. No between-group difference among the three footwear groups or condition by type interaction was found in any measured variables.

The results show that as shoe cushioning decreases, runners change their pattern of running to maintain constant external loads. The adaptation strategies to shoe degradation were unaffected by different cushioning technologies, suggesting runners should choose running shoes for reasons other than cushioning technology.

British Journal of Sports Medicine 2009;43:745-749