just hit the damn thing for 2 mins as hard as you can! Kick it, punch it, knee it what ever it takes to get you blowing and repeat that at least 5 times with a minutes rest inbetween. After that practice combo's for either a set amount of reps or time again the bag is only limited by the imagination good luck :Angel:
If you box, then try hitting it "all out" (with good form) for whatever round lengh youll be entering in. If not, 2 minutes is a good start. If you want some great conditioning, you could do some burpees, the asap after, hit the bag, then back to the burpees..repeat.
My personal favourite cardio routine with the bag is applying the Tabata method (20seconds all out, 10 seconds rest, repeat 8x equalling four minutes work) to the jab, cross, leg kick combo. I usually alternate the sides with each set, but it's still one hell of a workout
Jab x 50 Cross x 50 Left middle roundhouse X 20-30 Right middle roundhouse X 20-30 Take a 30 seconds to one minute break and start over, until you're worn out. Make sure you do a full motion jab and back to fighting stance, same with cross. Make sure not to drop your hands while kicking. Watch your technique while hitting the bag, it's more difficult than just hitting it constantly and will benefit you in the long run. As an important side note, don't hit it full force with your fists if you don't have handwraps and gloves.
I wouldnt advise timing how many punches your throw, just go all out on the bag! (with good form of course!) Seriously, I think you'd have more of a work out if you tried as much as you can with breaks in intervals, because one, your re-energising yourself at breaks so you can do more damage to the bag, two, your going to produce a far more better workout by training by feel and 100% commitment than a lousy kick on each side 50 times straight. Another good thing to encoporate your kickbag work with is circuit training, this could be: warm-up, stretches, bagwork, stretches, bodyweights, stretches, weights, more bagwork. Whatever your in the mood for, hell bring a mate along and do a little sparring
In my experience you're likely to do some damage to yourself if you really go a 100% on the bag, especially with bad form, since if you start wearing out and keep hitting the bag than you'll start doing mistakes - not closing your fists, pulling your shoulder\leg\whatever the wrong way, etc. It's not working 50% or even 30% on the bag isn't beneficial. Hell, it'll teach you to divide your strength and oxygen better for a round. But what do I know :\...
I do an MP3 bag workout downloaded from Iainabernethy.com. IMHO it's fantastic and ticks all the boxes. I rate it very highly. As it's an MP3 you don't need to look at a clock and can just go for it and concentrate on the job in hand. There's a variety of rounds (hands only, kicks only, close strikes, one minute continuous punching and lots more besides) and also a short video of Iain demonstrating what he means for you to do in each round if you're new to bag-work. It's twenty minutes long and works really well as a short cardio workout, warm up for other training or just a quick blast to clear the cob-webs. It's also structured with an integral warm up round to get you started. Warm up with 5 minutes of skipping whack it on your i-pod and got for it. (I've also just recorded my own tabatas timing MP3 that I'm going to christen at the gym tomorrow)
Read: http://www.rossboxing.com/thegym/thegym24.htm Watch: [ame="http://www.youtube.com/watch?v=0YFfy9lXFGE"]Heavy Bag Drills - RossTraining.com - YouTube[/ame]
Bas Rutten training cds 4 workouts from boxing, thai, mma and all around fighting can be done on a punching bag and very fun to do.