It’s important to be able to know how to warm up correctly to get the most out of your workouts, but without burning yourself out before the workout actually begins. A warm-up allows your body to adjust to your workout, preparing your joints and muscles for the heavier workload ahead and help reduce risk of injury. Most bodybuilders will either warm up to much or too little having the effect of either reducing your performance or just resulting injury.
I would first advise to raise your core body temperature before even touching a weight. This can be done through a short period of light cardio such as bike or cross-trainer. This will prepare your body systemically for the more intense exercise that is to come.
Now your body is warm, next is some light stretching. This will help prevent injury during a workout. Focus more on the areas you plan on working out that session.
Next is the actual warm-up, this is where many bodybuilders might overdo it, having the effect of burning out before the workout even begins and in fact reducing your recovery rate and muscle growth.
The amount of reps and sets you warm up with will generally depend on how heavy you intend to lift during your workout. For example, if you plan on bench pressing 60 kilos during your workout; start by pressing 20 kilo for about 10 reps and then slowly build up to your target weight in increments of around 15 – 20 kilo while decreasing the number of reps you do (20 Kilo X 9 Reps, 40 Kilo X 8 Reps, 50 Kilo X 7 reps etc…)
The above warm-up only involves 24 reps before the initial work set which prevents too much intracellular acid from building up and more efficiently prepares the central nervous system, muscles and joints for the heavy workload. The result will be a significantly improved performance on each work set, leading to a more productive and efficient workout.
As a general rule, more warm-up sets are required if you intend on lifting a heavier a load during your workout.