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Ok so lets face it, the bodyweight crowd out there doesn't really need to purchase any equipment that couldn't either be made or found, but presuming you're one of those people who wants all the latest and greatest gear, or just someone looking to add a few more tools to the toolbox and try something new. Here are a few pieces of equipment definitely worth looking into, and can add almost an unlimited amount of ideas and variation to your training regime.
So skipping the obvious tools like gloves, belts, straps, ipods, and nonsense of that nature lets choose to look at some of the best ideas out there that require little space, a small budget, and a bit of creativity. Going in no particular order I will give the pros and cons of some of the best equipment I have found out there, broken up into categories.

Pros: The sky is the limit with this piece and while not everything that can be done with this is difficult you can make up your own exercises or opt to intertwine the straps together and go from two grips to just one. The difference can be huge. I will say that bulgarian split squats, leg curls, flys, power pulls, and t's are personal favorites that can be made more or less challenging depending on the angle you are standing or leaning.
Cons: The price is a bit high for a piece of webbing and all the claims about it being created by a Navy Seal are extremely annoying. If you need ideas you can purchase DVD's, posters, or a virtual trainer, but again you are paying way more than you should be.
Elite RingsPros: if you think bodyweight training isn't difficult try holding an iron cross or doing a one arm chin (OAC). The rings add an element of instability that just can't be replicated with free weights. Looking to shore on some size to your shoulders, chest, and back, then flys, push ups, dips, chin ups, and even levers can do just that.
Cons- while not as expensive as the TRX these are not cheap given their simple nature, they are also a bit harder to set up if you're indoors and do not have a sturdy object to attach them too.

Pros- its almost half the price and is even lighter and more portable.
Cons- with price reflects quality, these things aren't as sturdy or as comfortable, but hey, who said exercising had to be comfortable.

Pros- They feel great, they loosen up sore areas, can help with thoracic mobility and they can be used for additional balance training.
Cons- For a piece of foam they aren't that cheap, but unless you want to buy a 6 inch PVC pipe which can be much less forgiving, or go the tennis ball route this is not a bad choice at all.
Myo Ball- essentially a mini, foam, gel, or air ball that may or may not have spikes that does essentially the same job as a foam roller. I like Perform Better's Spikey Ball.
Pros- the spikes get you even deeper, and feel amazing on tired feet.
Cons- the small ball takes longer to get your whole body.

Pros- the stick is much more portable than the previous tools, and can hit places that the ball and roller just plain can't.
Cons- couldn't really think of any, this isn't really necessary, if money is an issue stick with the foam roller.

Pros- this thing hits your muscles in a way that you have to experience for yourself, I will say that there is way more hip and adduction and abduction activation with the lunges. Push ups can be turned into flys, leg curls for the posterior chain, and as long as you have an open mind you can do all sorts of need ab-wheel variations too.
Cons- for 30 bucks I'd rather use towels on a hardwood floor, but since I don't have one at home I shelled out the dough and have really enjoyed using them, particularly with free weights.
Ab-Wheel- while there are a lot of variations out there such as the akro wheel, power wheel, ab dolley, I just plain prefer to use your standard 10 dollar ab wheelPros- it's cheap, it works, it's progressive, and it beats the snot out of crunches.
Cons- it may be difficult for some beginners, but remember you can do partials, negative, and rest/pause too.

Pros- the V Vest is way more sturdy than the X-Vest and uses nylon straps instead of elastic wraps to hold it on you, it also goes up to 100 lbs. The gravity belt is essentially a foam belt with weights on it, and it goes anywhere from 10 to 30 lbs. These are great for running, jumping, sports conditioning as well as all other traditional bodyweight exercises. The added weight also helps improve your passive respiration systems so it feels like you're training at a higher altitude.
Cons- these are extremely expensive and a burden to lug around if you don't plan on wearing them your entire training time. They also cost an arm and a leg for shipping so be prepared to spend more than you think.

Pros- if you haven't ever used a sandbag, you don't know how hard they can be. They're relatively safe to drop, you can throw and drag the bag too. They also require very little space to use, and things like shouldering are often times difficult to replicate with kettlebells, barbells and dumbbells.
Cons- the IFSS bag is very expensive for a piece of nylon and the filler bags are just as expensive. If you want to use the sandbag but don't want to knock out your pocket book, check around construction sites, I'm not saying steal the sandbags, but borrow them on a long term status, at night. Carrying them back home should be an expereince. You can also make your own using a duffel bag, or G.I. bag full of heavy plastic bags so you can separate the sand into appropriate weights.

Pros- they're fairly inexpensive last for quite a while, extremely portable, colorful and great for conditioning or power training.
Cons- you could just fill a basketball with sand, water, or sugar and patch it up. It would cost a whole lot less, and it's fairly inexpensive to make.
Products that are way too hyped up- now this is a bit argumentative for some to swallow but I will say that the stability ball, INDO Board, and particularly the BOSU ball are fairly worthless for anything real. The suspension system will give you the same strength and then some. While they might improve your balance, so does closing your eyes and standing on one foot. In my opinion of all that balance training is great for the older populations but it seems that most of the pros are against them because it is extremely difficult to add much resistance to particular movements. You'd be better off just squatting heavy.
So here's a few things worth purchasing if you have a little cash lying around and you're looking for a new challenge. This is not to say that these are the only good things out there, kettlebells, dumbbells and barbells can be excellent supplemental tools for bodyweight training.
Jason Kirby is an extremely creative personal trainer and strength coach. Find out more at All Around Strength.
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