The purpose of this study was to quantify relative contributions of impact interface, muscle activity, and knee angle to the magnitudes of tibial and femoral accelerations occurring after external impacts. Impacts were initiated with a pneumatically driven impacter under the heels of four volunteers. Impact forces were quantified with a force sensor. Segmental accelerations were measured with bone mounted accelerometers. Experimental interventions were hard and soft shock interfaces, different knee angles (0°, 20°, 40° knee flexion), and muscular preactivation (0%, 30%, 60% of maximal voluntary contraction) of gastrocnemii, hamstrings, and quadriceps. Greater knee flexion led to lower impact forces and higher tibial accelerations. Increased muscular activation led to higher forces and lower tibial accelerations. The softer of the two shock interfaces under study reduced both parameters. The effects on accelerations and forces through the activation and knee angle changes were greater than the effect of interface variations. The hardness of the two shock interfaces explained less than 10% of the variance of accelerations and impact forces, whereas knee angle changes explained 25–29%, and preactivation changes explained 35–48% of the variances. It can be concluded that muscle force and knee joint angle have greater effects in comparison with interface hardness on the severity of shocks on the lower leg.
Wolfgang Potthast, Gert-Peter Brüggemann, Arne Lundberg and Anton Arndt
Anton Arndt, Gert-Peter Brüggemann, Mikko Virmavirta and Paavo Komi
This study was concerned with identifying important flight characteristics of the ski jump at the end of the early flight phase and describing how these characteristics developed from the run-in through the takeoff and during the early flight phase. The K90 individual competition of the 1994 Olympic Winter Games was analyzed. The 2-D data (takeoff) were collected by a high-speed video camera, and the 3-D analysis (early flight) used an algorithm whereby two cameras followed the jumpers through the early flight phase. Center of mass (CM) velocities at takeoff and after early flight and CM heights at these positions had no significant linear correlations with total distance. Only small differences in these parameters were distinguished between better and poorer performers. Significant differences between jumpers were identified in angular parameters at takeoff and in early flight. A combination of five defined flight angles yielded an R 2 value of .84. It was found that the complex movement sequences involved in ski jumping were therefore more important in their contributions to optimal flight position than the ballistic properties of the ski jumper reduced to a single point model.
Anna Bjerkefors, Johanna S. Rosén, Olga Tarassova and Anton Arndt
Trunk, pelvis, and leg movements are important for performance in sprint kayaking. Para-kayaking is a new Paralympic sport in which athletes with trunk and/or leg impairment compete in 3 classification groups. The purpose of this study was to identify how physical impairments impact on performance by examining: differences in 3-dimensional joint range of motion (RM) between 10 (4 females and 6 males) elite able-bodied kayakers and 41 (13 females and 28 males) elite para-kayakers from the 3 classification groups, and which joint angles were correlated with power output during high-intensity kayak ergometer paddling. There were significant differences in RM between the able-bodied kayakers and the 3 para-kayak groups for the shoulders (flexion, rotation: able-bodied kayakers < para-kayakers); trunk and pelvis (rotation: able-bodied kayakers > para-kayakers); and legs (hip, knee, and ankle flexion: able-bodied kayakers > para-kayakers) during paddling. Furthermore, athletes with greater impairment exhibited lower trunk and leg RM compared with those with less impairment. Significant positive correlations were observed for both males and females between power output and peak shoulder and trunk flexion; trunk and pelvis rotation RM; and hip, knee, and ankle flexion RM. This information is important for understanding how key kinematic and kinetic variables for para-kayaking performance vary between athletes from different classification groups.