In order to improve muscular fitness, you should include _________.

To improve muscular fitness, incorporating the principle of overload is essential. This principle involves challenging your muscles by increasing the weight, resistance, or intensity of your workouts beyond what they are accustomed to. When you apply overload, your muscles are stimulated to adapt, grow stronger, and increase in endurance over time. This adaptation is a fundamental aspect of building muscular strength and fitness.

While flexibility exercises contribute to overall fitness and can support muscular performance, they do not directly target improvements in muscular strength in the same way overload does. Similarly, rest between repetitions is crucial for recovery and performance but is not a method for improving muscular fitness itself. The FITNESSGRAM is a fitness assessment tool rather than a specific method for enhancing muscular fitness. Therefore, overload stands out as the key factor in the development of muscular strength and endurance.