Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to build calf muscle without equipment [title] Do double-leg calf raises. [step] This is a classic exercise for toning and strengthening the calf muscles. This workout utilizes your own body weight instead of a weight machine to help build muscle mass.

Ending1: Unlike many exercises, double-leg raises only involve lifting weights at shoulder-level. [substeps] Place your feet on the ground beneath you on either a exercise mat or floor plate with a palm up. Ending2: When doing calf raises, hold a stationary dumbbell in your hands and swing your arms up so they're over your head. Perform calf raises over a soccer ball with your left leg, a volleyball with your right knee, or a giant golf tee with your left foot. Ending3: [substeps] Begin by doing this exercise doing one set of 10 to 20 squats with a set of 10 to 15 squats in between. Then do five or six sets for each leg. Ending4: It strengthens both the gastrocnemius and soleus muscles. To start off, you will need to stand near a wall to balance yourself, if needed, and your feet should be hip-width apart with your ankles, knees and hips vertically aligned.

Answer format: ending1/ending2/ending3/ending4