Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to strengthen quads using a fitness ball [title] Practice all leg moves over a padded mat. [step] Because it takes time to get comfortable balancing on the fitness ball, practice each move on an exercise mat to cushion your fall and help your wrists support your weight more comfortably. [title] Engage your core muscles with each exercise.

Ending1: [step] When you feel your muscles contracting, loosen them to help you move your hips. Push your hip bones back and control the movements as much as possible. Ending2: [step] Muscles are the most sensitive muscle group and a fluid, constant contraction helps to keep those muscles engaged and reduce stress. [title] Exercise your inner thighs with the exercise mat. Ending3: [step] By tightening your abs and back as you work your quads, you can help stabilize yourself and tone your core as you work out. [title] Perform traditional squat moves for the quadriceps. Ending4: [step] Do cardio, strength-ups, and push-ups on a weight bench or a bench that is elevated at least 30 feet (4.7 m). Be careful not to strain when doing weight-lifting.

Answer format: ending1/ending2/ending3/ending4