What type of training is likely to increase muscle pennation angle?

The increase in muscle pennation angle is primarily associated with heavy strength training. When individuals engage in this type of training, the muscle fibers adapt by altering their structural arrangement. A greater pennation angle allows for a higher density of muscle fibers to be packed into a given area, which can enhance the muscle's ability to generate force.

Heavy strength training stimulates the recruitment of motor units and promotes muscular hypertrophy, leading to changes in muscle architecture. These adaptations are driven by the specific mechanical demands placed on the muscle during resistance training exercises, such as squats and deadlifts. The increased pennation angle can lead to greater force production capabilities, making it particularly relevant for athletes looking to improve their strength and power output.

In contrast, light endurance training, cardiovascular training, and flexibility training focus more on endurance, aerobic capacity, and range of motion, respectively. These training modalities are less likely to induce the specific structural changes associated with an increase in muscle pennation angle. Therefore, heavy strength training is clearly the most effective choice for promoting this adaptation in muscle anatomy.