An abdominal crunch is an effective stomach-strengthening exercise. If your body shakes when you perform crunches, you are doing the exercise correctly. When your muscles are strengthened, the muscle tissue contracts and releases. This motion can appear shaky, or as a trembling sensation until your muscles become accustomed to the exercise. As you perform the crunch and your muscles fatigue, you might experience a stronger shaky sensation. If you can work through this feeling, continue your crunch. If the shaking stops your workout, you need to modify your body position or your timing.
Raise your feet off the floor with your knees bent as you perform the crunch to reduce the strain on your hip muscles.
Cross your arms over your chest instead of placing them behind your head to reduce the resistance during your crunch.
Rest your feet on a couch or chair to reduce the strain on your lower abdominal area during a crunch.
Keep your hips still during a crunch and only move your upper body.
Stretch your abdominal muscles between sets of crunches. Lie on your back and raise your arms over your head. Straighten your legs and reach away from your body with your fingers and toes. Hold the stretch for 15 to 30 seconds. Turn over to lie on your stomach. Place your hands underneath your shoulders. Straighten your arms to lift your upper body as you keep your hips on the floor. Maintain the stretch for 15 to 30 seconds.
Reduce the number of crunches you perform at once and increase the number of sets to reduce stomach muscle fatigue.
Increase the amount of rest time you take in between sets of crunches, such as increasing from 60 seconds to 90 seconds.
Reduce the number of days a week you perform crunches and allow for a day of rest in between abdominal workouts.