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If you rush into the splits, you may hurt yourself. You must stretch before you do the splits even if you have done the splits a hundred times. Stretching your muscles will help you to ease into the splits more carefully. Do each stretch a few times repeatedly, so to increase flexibility in those stretches. If you want to follow a specific program, try physiotherapist Lisa Howell's flexibility program called The Front Splits Fast.
Stretch before you do the splits. Do a 10 to 20 minute warm-up, stretching each of your muscles.