1 - Do them first as most people skip abs and calves. Some trainers will prescribe the ab work and calf work first as they are commonly neglected body parts.

3 - "Work the weakest body part first", as long as it doesn't adversely effect other body parts you might work that day. If your abs are lacking, then you'd certainly want to focus on them and work them first while your energy and focus is highest.

5 - Timing doesn't matter. Consistency is the key. Doing them is more important then when you do them.

So what is correct'A study done in the January 2007 issue of Muscle and Fitness found that a group who performed a 6 rep max squat set did significantly less weight if they trained abs before doing the squats.

If your abs and core are fatigued from previous exercises, it can cause weakness on subsequent exercises and increase the risk of lower back injury.

Those concerned with their abs or if your abs are a weakness, you can do additional work on non-weight training days (some people do them after cardio to keep them separate from weight training sessions).

Why would you fatigue your triceps before doing chest work?You wouldn't.

While I agree the level of core work depends on the abilities of the individual there's still NO physiological reason yet that clearly describes a situation in which case doing core work BEFORE your workout is beneficial other than a time saver, your fresh or "do it first so you don't forget it".

"On the days when you are doing weight training exercises for your other body parts (legs, arms, back, chest, shoulders), always do your abs and core routine after the rest of your weight training so that you're not training the rest of your body with a fatigued core and stabilizers."