Study on Counter Movement Jump Performance in a Force Platform – Part 2

Results

The total height of the jump performed was 0.2446 m with the impulse and velocity of 152.8503 and 2.1908 m/sec respectively.

Ground reaction forces

Ground reaction force in the Z direction is positive throughout the jump with a little drop at the beginning of the take-off phase which then increases linearly and again slowly drops to the point of zero at the end of take-off phase. GRFz remained zero during the time period in the air and it rises to the maximum (8.32N/kg) on landing and slowly drops down (fig. 1.c.). Ground reaction force in the X direction is neutral throughout the jump with a slight back and forward movement before take-off and slight backward movement in the beginning of landing and then a body is pushed forward during landing (Fig. 1.a.).

There is slight sideways movement seen before the take-off and some error in the calculation of ground reaction force in Y direction during landing and recovery phase (Fig. 1.b.). Due to the oscillatory forces produced on the force platform, errors were seen during the landing phases in the result of GRF in all directions (Fig. 1. a, b, & c).

Joint Angles (Ankle, Knee, and Hip)

The ankle angle is significantly reduced (1.40 rads, lowest angle) during countermovement at the lowest point of preparation showing dorsiflexion which is again markedly increased with plantar flexion during push-off up to the take-off point. Ankle remains plantar-flexed more of the time in the air and is markedly dorsiflexed (1.38 rads) before landing and during landing (Fig. 2.a.). Similarly, significant knee flexion is seen from the start of countermovement up to the lowest point of preparation which is increased significantly while extension of knee up to the final point of contact before take-off (fig 2.b.). However, the knee is not flexed markedly during landing in-comparison to ankle dorsiflexion.  Hip extension is maintained (lowest 1.98 rads, during countermovement) in comparison to ankle and knee throughout the jump (fig 2.c.).

Joint Moments (Ankle, Knee, and Hip)

The ankle moment is negative throughout the jump with error seen during the landing phase of the jump (fig.3.a.). The knee moments are positive in the beginning of countermovement and before takeoff (fig 3.b.). Hip moments are neutral with slight negativity throughout the jump (fig 3.c.). Moreover, the peak joint moment is greater for ankle and knee which is coincided with the change of direction of a center of mass from the downwards movement of the body to the early phase of upward movement of the body. Some errors are seen during landing phase possibly due to oscillatory forces in force platform and noise (fig 3. a, b & c).

Joint powers (Ankle, Knee, and Hip)

The joint powers (ankle, knee, and hip) are positive before the takeoff phase while maximum power is generated by knee joint during push-off phase to lift the body vertically upward (fig 4.b.). Similarly, power generated by ankle is higher in compared to hip power. However, the power output of hip joint become positive earlier than ankle and knee suggesting the early onset of hip extension during push-off phase (fig 4. A, b & c).There are some errors in the calculation of joint powers in the landing phases. In the rest of the phases of the jump; ankle, knee and hip powers are in a neutral line.

Figures and Descriptions