How to strengthen your legs ?

Exercise them with an activity such as walking, jogging weight-lifting or swimming.

Lift your hips and pull your feet underneath you. Return to starting position and repeat. Curtsey lunge: Standing with both feet shoulder width apart, take your left foot and take a big step behind and across your right leg. Bend your knees, lowering your body until your front thigh is almost parallel to the ground.

Get a push mower and use it. All that stop and go stuff and turning this way and that way is good for the whole body.

Lift heavy cans of spam will build muscles.

You can jump on the trampoline it can helps to build your legs strength and core muscles as you need to maintain good posture and balance while tramplining. Your leg muscles are also exercised as you jump up and down on a trampoline. Your quadriceps, hamstrings and calf muscles are all used to push you off the trampoline and to absorb your weight as you land. Unlike other jumping exercises, such as skipping rope, tramplining reduces the amount of impact on your knees and ankles, making the exercise safer than other options.

For strengthening of legs, there is no effective exercise as squats. Apart from that Step up exercise is also effective in which a box or a step is used all you need to do is step up with one leg and back down, alternating legs.

You can do Cycling, Jogging, Pushup, and Squat, Eccentric Calf Raises, Bent-Knee Calf Raise, Straight-Leg Calf Raise.
These are the few exercises that you can try according to your energy level.