This thesis is presented as a series of four empirical studies. The studies measured and examined the isokinetic force ratios of the knee extensors and flexors and investigated the effects of strength training on force production, ratios and subsequent power output during maximal activity in men and women. The initial study gathered preliminary data regarding isokinetic force values and strength ratios of the knee extensors and flexors in rugby league players. Values for rugby league players were within previously reported ranges but the usefulness of the ratios obtained was questioned. The second study therefore investigated the dynamic control ratio. The dynamic control ratio was compared with the traditional hamstrings/quadriceps strength ratio in rugby league players at three velocities. The dynamic control ratio was higher than the conventional ratio, and the difference increased as the velocity of measurement increased. The dynamic control ratio more closely represented normal functioning and highlighted the role played by the eccentrically acting flexors in controlling the opposing knee extensors. The third investigation examined the influence of strength training on force production and the subsequent production of peak and mean power. After 12 weeks of strength training men and women had significantly increased isokinetic force production. This was mirrored by an increase in peak power output. There were also increases in work done during a maximal isokinetic test suggesting that strength training improves the ability to perform anaerobic activity and may positively enhance anaerobic capacity. Finally, strength training was analysed for its effect on muscle quality using simple ratio or power function ratio measures. Improvements in muscle quality will be potentially masked if simple ratios are used. If leg volume is raised to the power 0.67 then muscle quality in men and women is similar. This is the case for isokinetic force and anaerobic performance.