A good warmup is an essential element of any workout and crucial to success in competition. Studies suggest that 15-20 minutes of low to moderate intensity effort (50%-60% of maximum heart rate) can increase endurance performance by 6% and sprint performance by 7% (compared to no warmup). Some studies are now even showing that higher outputs in the 70-90% range during warmup actually harm performance. Make sure that you are warming up enough by checking your heart rate throughout warmup. Once you have reached a sustained heart rate in the 50%-60% of maximum, you are probably ready for competition or the more intense portions of your workout.