These are 3 good and simple exercises to make your abdomen really strong and to make your core fit: "Knees-up", "Classic crunches", "Side plank": you can do them in a row or you can perform them separately: anyway, you should do a total of 10-12 sets of 10-12 reps with just 5 secs of rest between sets...Eat good and train your abs every day, mixing all these 3 exercises in different ways.
A 4 minutes workout: 15 pull-ups+20 GOOD push-ups, then 10 push-ups+20 push-ups, than as many as possible of both till Oasis finish their LIVE FOREVER (and me my ENERGY...):-)
The correct way to do pull ups without hurting your shoulders: start with your deltoids very close to your ears, then go for the concentric phase with a fast movement, then go for the eccentric phase, more slowly and without letting the deltoids touch your ears again ......repeat 12 times for 3 series with 45 seconds rest between the series
A fast, effort-requiring training of just 4 minutes...great lactate build-up both for the back and for the front muscles of the entire torso: 12 pull ups followed by 25 push ups then as many as possible pull ups then again as many as possible push ups, 6 times around...