Some exercises should be avoided because they can cause damage to bones, muscles and surrounding tissues (musculoskeletal injury). They may make it more likely that you will injure yourself or worsen a pre-existing injury or medical condition.
Bouncing while stretching
Ballistic stretching uses the momentum of the body part in an attempt to force it beyond its normal range of motion. (e.g. bouncing down repeatedly to touch your toes.). It is not recommended because it can cause muscle tears and soreness. Try the alternate slow, sustained stretches and hold them for 10-20 seconds.
Standing toe-touches
This exercise places an unnecessary strain on the lower back, as the exercise is often performed quickly in the belief that it stretches the leg and lower back muscles. An ideal alternative to this exercise can be performed simply by sitting on the ground and slowly reaching forward to touch the toes. Concentrate on slow, sustained stretches and Hold the stretch for 10 to 20 seconds.
Full squats
Full squats, either with or without a barbell or weight held across the shoulders or in the hands, pushes the knee joint past 90°. This may strain the ligaments, cartilage and muscle of the knee joint and/or lower back. Go for parallel squat instead.
Double leg raises
This exercise involves lying on your back and raising both legs at the same time. This places enormous stress on the lower back. Another potentially harmful variation is to lie on your stomach and lift both legs at the same time. Try the variation as one leg raise.
Isometric exercises
Isometric or static exercises (tensing the muscles against an immovable object) are generally unsafe for older adults as this type of exercise places enormous pressure on the heart and can raise blood pressure. Under qualified supervision however, certain isometric exercises may be prescribed.
Holding the Breath
By holding the breathe when performing an exercise the pressure within the heart and blood vessels increases, which can cause undue stress on the heart, circulatory system and dizziness. To avoid this try to breath deeply and as controlled as you can make it.
At the end I would just suggest to avoid or modify any exercise that causes you pain or discomfort.