Legs don't have strength. On single leg.

Quad Clenches: Lie flat on your back or sit upright on a chair with leg kept horizontally on another surface. Now, tighten the muscle on the front of the thigh by pushing your knee down. You should feel your thigh muscles clench, Hold for 3 secs. Repeat 10 times twice a day. Short Arcs: Lie flat on your back or sit upright with your leg placed horizontally on a flat surface like a chair or bed. Place a rolled up towel under the knee. Pull your toes towards you and clench you thigh muscles. Slowly lift your foot up off the bed until your knee is straight (keep your knee resting on the towel). Hold for 3 secs and slowly lower them on the chair. Repeat 10 times twice a day. Straight Leg Raise: Lie flat on your back. One leg and knee will be straight and other leg should be bent. Pull your toes towards you and tighten/clench the muscle on the front of the thigh, locking your knee straight. Lift your foot up in the air, about 6 inches off the bed. Hold for 3 secs and slowly lower the leg. The knee must remain straight the whole time you are doing this exercise. Hamstring stretching Towel Hamstring Stretch Lie on the back, supporting the thigh with the hand or with a towel wrapped around it.. Slowly straighten the knee until a stretch is felt in the back of the thigh, trying to get the bottom of the foot to face the ceiling, one leg at a time. Hold the position initially for 10 seconds, and gradually work up to 20 to 30 seconds. Seated Hamstring Stretch While sitting at the edge of a chair, straighten one leg in front of the body with the heel on the floor. Then, sit up straight and try pushing the navel towards the thigh without leaning the trunk of the body forwards. Hold this stretch for 30 seconds Repeat 3 times for each leg.

It may be because of loss of electrolyte / water , usually happens after a heavy workout. But, If you are facing the symptoms daily , Please, get your serum electrolyte check and also get a DEXA scan Done (that is for (BMD) Bone Mineral Density) and post tests as per the reports you may start with the essential electrolytes and some strengthening program depending upon BMD .

Please get your tests done as soon as possible. and Prevent falling , by being cautious.

STAY HEALTHY