I am always asked when do you stretch.  I say at end of your workout. Then asked why? When you stretch cold muscles is very easy to pull a muscle or get injured, especially with strength training.

Safe way to your workouts:

• Start all workouts with easy cardio warm up of 5-10 minutes.
• Strength train or increase cardio intensity.
• Cool down with easy cardio for 5-10 minutes. If you did strength training and want to lose fat/weight, do cardio for 20 minutes which will continue burning fat.
• Stretch at end of workout. Hold the stretch position for 20-30 seconds. Don’t bounce.

Have a good workout!