We had a taster session on Wednesday here at the University of Sunderland where we looked at the relationship between strength, power and velocity.
Strength was determined as torque production when performing a knee extension/flexion at 60 degs/s on our Biodex System 3 isokinetic dynamometer.
Speed was determined by 10m sprint timed using two sets of Brower timing gates. Time was used rather than speed to give an example of negative correlations in Table 2.
An index of power was determined from vertical jumping performed using vertical jump mats. Subjects performed a counter-movement jump with their hands by their sides. We could use the Lewis equation (1981)to calculate the average power produced during this exercise.
Predicted power (watts) = 21.72 x subject mass (kg) x square root of the jump height (m)
And finally a measurement of lower limb velocity (ankle) during a functional movement (kicking a football) was made from a single marker using our Vicon 3D analysis System.
Football strike captured in our Biomechanics lab
This system uses markers placed on the body and an 8 camera setup to track the movement of these markers in 3-dimensional space during the movement. Through the use of Vicon software ankle velocity was recorded.
Table 1 contains some of the raw data from four of the subjects (with permission).
Table 1: Measures of lower-body strength, power and speed.
| Leg Strength | Vertical Jump Height (m) | 10m Sprint Time (s) | Ankle Velocity During Football Kick (m/s) | ||
| Name | Quadriceps (Nm) | Hamstrings (Nm) | |||
| Average | 160.8 | 91.5 | 0.43 | 1.93 | 11.6 |
| Max | 226.9 | 168.7 | 0.49 | 2.20 | 12.6 |
| Min | 89.2 | 25.0 | 0.37 | 1.81 | 9.8 |
| Andy | 176.5 | 94.8 | 0.49 | 1.81 | 11.6 |
| Mike | 150.5 | 77.5 | 0.41 | 1.82 | 12.5 |
| Phil | 226.9 | 168.7 | 0.46 | 1.88 | 12.6 |
| Jo | 89.2 | 25 | 0.37 | 2.2 | 9.8 |
As we can see, sprint speeds ranged between 4.5 and 5.5 m/s.
Table 2: Correlation coefficients between these parameters:
| Leg Strength | Vertical Jump Height (m) | 10m Sprint Time (s) | Ankle Velocity: Football Kick (m/s) | ||
| Quadriceps (Nm) | Hamstrings (Nm) | ||||
| Quadriceps Torque (Nm) | 1.00 | 0.99 | 0.81 | -0.74 | 0.83 |
| Hamstrings Torque (Nm) | 0.99 | 1.00 | 0.72 | -0.63 | 0.80 |
| Vertical Jump Height (m) | 0.81 | 0.72 | 1.00 | -0.77 | 0.58 |
| 10m Sprint Time (s) | -0.74 | -0.63 | -0.77 | 1.00 | -0.89 |
| Ankle Velocity: Football Kick (m/s) | 0.83 | 0.80 | 0.58 | -0.89 | 1.00 |
Correlations
At its simplest, a correlation is a measure of the relationship between two variables. For a more lengthy description of what correlations mean go to this website. As we saw, correlations between hamstring and quadriceps strength was very good (R = 0.99), indicating the not unsurprising fact that those with stronger hamstrings also tended to have stronger quadriceps. An example of a negative correlation was found between quadriceps strength and 10m sprint time (R=-0.74). This is a negative correlation because those with the strongest quadriceps tended to have the shortest 10m times (because they were the fastest).
Comparing all measures to our ‘functional’ movement of kicking a football it was clear that lower limb strength was strongly linked to how hard the participants could kick a football (R=0.83 and 0.80) but less so to vertical jump performance (R=0.58). Again this is unsurprising because the movement pattern is more similar between knee extension/flexion and kicking a football compared to a vertical jump and kicking a football. This is despite the fact that the angular velocities when kicking a football are markedly greater than the angular velocities when performing a knee extension/flexion exercises (set at 60 deg/s).
content.
