In generating ball-speed (B-V) for the instep-kick, football players primarily need high
hip-flexion (HFV), and greater knee-extension velocities (KEV). Both factors significantly
influence foot-velocity (F-V). Appliance of the kinetic-chain concept within the instep-kick
requires optimal dynamics of proximal to distal segments, to facilitate the kinetic-energy
transfer via high torque moments within a rapid timeframe. Kinetic-energy transfer is
transferred from the decelerating system mass (planting of the support-leg), followed by elastic
energy transference via the hips and through to the kicking-leg. Research on the contribution
of the support-leg in recent years has yet to preclude the significance of leg-stiffness (KLEG)
within kicking techniques. leg-stiffness is a concept usually concerned with running and
hopping, characterising efficiency of elastic energy within leg function, and is the peak ground
reaction force (FMAX) divided by the change in leg-length (∆L). Instep-kick association with
the KLEG concept affords research toward enhancing training regimens. Improving support-leg
function may serve as a passive technique contribution within competition environments to
those already highly skilled in dead-ball kicking scenarios. Hence, the purpose of this study is
to determine the relationship between KLEG and the factors leading to B-V. Nine participants
(N=9, age 21.2±1.0-yrs; mass 82.3±11.1-kg; height 183.0±6.8-m), playing at a university and
semi-professional level were tested using kinetic (1000 Hz) and kinematic (500 Hz) systems
over hopping and kicking tasks. Pearson’s product-moment correlation determined
relationships between variables and task specific KLEG – (hopping-KLEG, and kicking-KLEG).
Hopping-KLEG was found to have a significant negative moderate correlation with HFV (rp=-
0.403, p=.010), and KEV (rp=-0.328, p=.044). However, the variance in changes of leg-length
of the kicking task (kicking-∆L) among a small sample size (n=7) influenced results
substantially, in that, analysis of participant specific data suggests that the vertical displacement
of hip-joint centre (HJC) and ground reaction force (GRF) variance within low sample sizes
fracture results excessively: values of hopping-KLEG and kicking-KLEG reveal a standard
deviation ~30% and ~70% from the mean, respectively. Also, when comparing this study’s
results to the reported literature, the small sample size returned reliable data with significant
correlations in all combinations of: B-V; F-V; HFV; and KEV, implying reliability of results.
In conclusion, this study disqualifies further investigation into the relationship between KLEG
and the factors leading to B-V.