Which of the following is solely a muscle-strengthening activity that can be done at school: sit-ups?

Sit-ups are indeed solely a muscle-strengthening activity. They primarily target the abdominal muscles but also engage the hip flexors and the muscles of the lower back. Sit-ups can be performed virtually anywhere, including at school, which makes them a convenient exercise for students who want to strengthen their core muscles.

Muscle-strengthening activities are essential for a balanced workout routine. They help build muscle mass, improve muscle strength and endurance, and can support bone health. Strength training can also increase metabolic rate, which aids in maintaining a healthy body weight.

In addition to sit-ups, other muscle-strengthening activities include push-ups, squats, lunges, and weightlifting exercises. These exercises typically require the muscles to work against a force, such as gravity or the resistance of weights, bands, or body weight.