The percentage of time you spend doing high rep workouts completely depends on the discipline or sport you enjoy most. Getting ready for a cross-country bike ride? Perfect. Your muscles will be able to store more glycogen -- which your body will use for your energy -- if you incorporate plenty of high repetition strength training into your fitness plan. Planning to compete in a marathon? The increased number of capillaries created by all those repetitions will allow plenty of oxygen to get to your muscles and power you through those trying miles. Want to win a power lifting contest? You'll need to focus the majority of your time on heavy weight and low repetitions (1 to 5), which force the body to recruit all muscle fibers to create optimum power [source: Norton]. A bodybuilder would fall somewhere between the endurance athlete and the power lifter. He'll see the most growth if he focuses on moderate reps (6 to 12) while not ignoring the indirect value of lighter and lengthier sets [sources: Venuto, Norton].
If you're more interested in looking good at the beach than competing in a sport, ask yourself which of the above athletes would you prefer to look like? After all, it's all a matter of opinion, and you certainly don't have to have a medal around your neck to get a date.