Introduction
The quadriceps muscle group is made up of four muscles: the vastus lateralis, vastus medialis, vastus intermedialis and the rectus femoris. These muscles allow extension of the leg to occur during concentric contraction. The stronger the contraction produced by the muscles, the greater the force produced by them. You can measure the force produced by the muscle by measuring the velocity with which they contract. This is due to the force-velocity relationship. Kent (2006) explains this relationship by saying that if the velocity of the contraction is high, the force generated by the muscle is low, and vice versa. This is because if the velocity of the contraction is high, the muscle has less time to recruit muscle fibres to engage with the contraction.(Narici., Roi., Landoni., Minetti & Cerretelli. 1989). To measure this relationship in vivo, the method used is to measure the torque-angular velocity by using a isokinetic dynamometer. This enables measurement of the torque produced at the knee joint while the identified muscle group contracts at various velocities. In order to produce a greater force with the muscles, you need to increase the size of the muscle by training the muscle are, causing hypertrophy, increasing the size of the muscle fibres allowing more force to be produced (Widmaier., Raff & Strang. 2006). This has been shown by (Zakas., Mandroukas., Vamvakoudis., Christoulas & Aggelopoulou. 1995), as higher division professional basketball players achieved greater peak torques in their quadriceps muscles than lower division players. A study carried out by Cress, Peters & Chandler. (1992) showed that the force of concentric muscle contractions of the quadriceps decrease as the velocity increases but there is no change in the force produced when the velocity increases with eccentric contractions. The aim of this study was to compare the force-velocity relationship of the quadriceps muscle between sports & exercise science students and elite sprinters. It could be predicted that the force-velocity relationship will be greater for the elite athletes but the relationship will follow the same trend. Methods Seven Sports & Exercise Science students and six Elite sprinters were asked to sit in a Humac Norm isokinetic dynamometer to perform the experiment. Once in the dynamometer, the seat and the hip-knee adapter were adjusted to line the adapter up with the centre of rotation of the knee – the lateral epicondyle of the femur and also, the participants knee was positioned two fingers width from the chair while in flexion to allow optimum flexion to occur. The hip-knee ad was placed just above the ankle whilst in dorsi flexion so that the foot didn’t contribute to the lifting. The straps were then placed cross the body and on the thigh of the working leg, tightly enough so that the leg stayed in position, but not too tight that the resistance aided the exercise. The dynamometer was then set up to each particpants range of moton to prevent injury to the participant. The subjects were then asked to perform 3 maximal isometric contractions at 60° of flexion, followed by 5 maximal repetitions for each isokinetic contraction (60°, 120°, 180° and 240° (concentric only) degrees per second). They performed these exercises with their arms cross over their chest. The peak torques were recorded for each contraction and were then calculated to form a mean. The mean values were then calculated as a percentage of the isometric contraction score. These results were then plotted on a graph. Results
Figure 1 shows the force-velocity relationship for the two sample groups. The figure shows that the elite sprinters on average had greater peak velocity percentages at each of the isokinetic contractions. The trends for the two sample groups are different at eccentric contraction. During eccentric contraction, the sport science curve generally stays straight; however, the elite sprinters curve goes up during eccentric contraction, showing greater force produced at lower angular velocities. The trends for concentric contraction are the same for both samples, the peak torques decreasing as angular-velocity increases.

Table 1- Percentages of normalised peak torques compared to the isometric contraction at different angular velocities for seven Sport & Exercise Science students Normalised peak torque- Sport & Exercise Science | | | | | | | | | | Normalised peak torque (% of isometric) | | | Angular Velocity (deg/s) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | Mean | SD | Eccentric | -180 | 72 | 83 | 73 | 78 | 75 | 86 | 80 | 78 | 5 | | -120 | 69 | 87 | 64 | 86 | 67 | 88 | 90 | 79 | 11 | | -60 | 72 | 80 | 70 | 86 | 91 | 87 | 101 | 84 | 11 | Isometric | 0 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 0 | Concentric | 60 | 80 | 75 | 59 | 64 | 77 | 72 | 66 | 70 | 8 | | 120 | 71 | 72 | 55 | 59 | 54 | 51 | 52 | 59 | 9 | | 180 | 60 | 66 | 48 | 50 | 45 | 44 | 51 | 52 | 8 | | 240 | 60 | 57 | 41 | 40 | 47 | 40 | 42 | 47 | 8 |

Table 2- Percentages of normalised peak torques compared to the isometric contraction at different angular velocities for six elite sprinters

Normalised peak torque- elite | | | | | | | | | Normalised peak torque (% of isometric) | | Angular Velocity (deg/s) | 1 | 2 | 3 | 4 | 5 | 6 | Mean | SD | Eccentric | -180 | 78 | 83 | 69 | 100 | 78 | 82 | 82 | 10 | | -120 | 103 | 110 | 103 | 112 | 108 | 104 | 107 | 4 | | -60 | 117 | 130 | 118 | 124 | 116 | 114 | 120 | 6 | Isometric | 0 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 0 | Concentric | 60 | 91 | 88 | 91 | 94 | 91 | 95 | 92 | 3 | | 120 | 84 | 83 | 83 | 85 | 86 | 87 | 85 | 2 | | 180 | 73 | 73 | 77 | 75 | 78 | 77 | 76 | 2 | | 240 | 59 | 64 | 70 | 69 | 68 | 71 | 67 | 5 |

Figure 1- a scatter graph showing the force-velocity relationship of the quadriceps muscles of Sports & Exercise Science students and Elite sprinters

Discussion
The results show that the elite sprinters had a greater mean percentage of their isometric contraction peak torque for each of the isokinetic movements than the Sport & Exercise Science students. This is because the elite sprinters are trained so they can achieve a greater peak torque than untrained participants (Andersen et al., 2005). This is because the trained elite sprinters will have a greater muscle fibre size and an increased neural drive to the muscle (Narici et al., 1989) so they will be able to recruit more muscle fibres, therefore, able to produce a stronger contraction, in turn increasing their peak power production (Kraemer et al., 2002). The force-velocity relationship shown by the sprinters for eccentric contraction opposes that of the study by Cress, Peters & Chandler. (1992). This study shows that the torque produced by the eccentric contrction doesn’t vary with velocity, yet this study suggests that with elite athletes, the torque of eccentric contractions increases as the velocity lessens. Both samples show that the eccentric contractions produce more torque than the concentric contrctions. This is due to more fast twitch fibres being recruited during eccentric contraction, allowing a greater torque to be produced (McHugh., Tyler 2002). The reason why the torque increases as velocity decreases with concentric contraction is because when there is a greater load placed on the muscle – the slower velocities- more myosin-actin cross-bridges are formed in order to move the load, requiring more time to contract so the velocity decreases. The main limitation to using the isokinetic dyanometer and this method is the fatigue that the particpant may experience towards the end of the experiment (Cress, Peters & Chandler. 1992). as each movement is at maximal intensity.

Andersen, L. L., Andersen, J. L., Magnusson, S. P., Suetta, C., Madsen, J. L., Christensen, L. R. & Aagaard, P. (2005) Changes in the human muscle force-velocity relationship in response to resistance training and subsequent detraining. Journal of Applied Physiology, 99, 87-94.
Cress, N. M., Peters, K. S. & Chandler, J. M. (1992) ECCENTRIC AND CONCENTRIC FORCE-VELOCITY RELATIONSHIPS OF THE QUADRICEPS FEMORIS MUSCLE. Journal of Orthopaedic & Sports Physical Therapy, 16, 82-86.
Kraemer, W. J., Koziris, L. P., Ratamess, N. A., Hakkinen, K., Triplett-McBride, N. T., Fry, A. C., Gordon, S. E., Volek, J. S., French, D. N., Rubin, M. R., Gomez, A. L., Sharman, M. J., Lynch, J. M., Izquierdo, M., Newton, R. U. & Fleck, S. J. (2002) Detraining produces minimal changes in physical performance and hormonal variables in recreationally strength-trained men. Journal of Strength and Conditioning Research, 16, 373-382.
McHugh, M. P., Tyler, T. F., Greenberg, S. C. & Gleim, G. W. (2002) Differences in activation patterns between eccentric and concentric quadriceps contractions. Journal of Sports Sciences, 20, 83-91.
Narici, M. V., Roi, G. S., Landoni, L., Minetti, A. E. & Cerretelli, P. (1989) CHANGES IN FORCE, CROSS-SECTIONAL AREA AND NEURAL ACTIVATION DURING STRENGTH TRAINING AND DETRAINING OF THE HUMAN QUADRICEPS. European Journal of Applied Physiology and Occupational Physiology, 59, 310-319.
Zakas, A., Mandroukas, K., Vamvakoudis, E., Christoulas, K. & Aggelopoulou, N. (1995) Peak torque of quadriceps and hamstring muscles in basketball and soccer players of different divisions. Journal of Sports Medicine and Physical Fitness, 35, 199-205.