Back pain may occur at any time and its occurrence in many cases is unexplainable. Nevertheless, any back pain should be taken seriously as it can be quite debilitating. Normally, your back (particularly your lower back) will be involved to some degree when performing most exercises, especially those that involve standing. This is why it's important to strengthen your core muscles (your lower back being one of them) in order to maintain postural integrity. In fact, poor posture due to weak core muscles may exacerbate back pain as a result of muscular imbalances.
If you experience back pain (especially lower back pain) while exercising, do NOT be alarmed. Your lower back is essentially the link between your lower and upper body. As such, the erector spinae muscles need to be strong to withstand the daily strains that occur. Remember that dull aching pain is normal and you need not be concerned with this when performing exercises like the squat, deadlift, lunges, etc. But if you feel sharp pain that feels severe, then it's time to take a break and give your back some time to heal and recover. See other articles elsewhere within this blog for tips on treatment for back pain. There may be particular exercises that simply don't work for you and seem to aggravate back pain. If this is the case, avoid doing them. Maintaining good posture is extremely important when executing exercises and if at any time your posture becomes compromised, this may be the cause of your back pain.
BOTTOM LINE: Listen to your body! Know the distinction between good and bad pain. Always be aware of your posture when performing exercises and when in doubt, either seek tips from a professional personal trainer or else refrain from doing the exercise.
Brian Danley, CFT
"Motivation is what gets you started. Habit is what keeps you going."