I be a very fit , small frame woman , early 50 's and think the ShakeWeight could strengthen my upper arm . as a result of use this device I have sustain a pinch nerve in my neck and tear both rotator cuff , I have my left arm in a sling for the past 4 week . I go to BB&B; , to check out the ShakeWeight in person ; I look at the woman size first , and find it disappointingly light and wimpy ; and it just do not seem like it could do the job ; so I decide to buy the man 's ; which be double the weight , I guess I be not as fit as I think , I do give it a go , work with it 3min a day to start off nice and easy . that little 3 min a day work out kick my butt ! after the 2 first 30 seconds set ; I be out of breath ; I start burn after the third day , decide to work through the pain a fourth day . that night ; I sleep very badly and wake up completely stiff the next morning . I could not turn my head one way or another , then both my shoulder joint be burn , and the pain just get worse every day until I could not function normally anymore ; I be apply a ice pack several time a day . even though I be take a anti-inflammatory ; the pain be like a white hot poker burn through my neck , chest and shoulder . a week later ; I be actually scream in pain and cry like a little child until one of my neighbor bring I a couple of Percocets and a heating pad , which really get I over the worst of it , until I could get to a doctor ; I could not do the basic thing we all take for grant , like brushing my tooth , wash my hair or apply moisturizer to my face or body or even drive for a whole month . imagine not be able to pull you own pants up after go to the toilet ! impossible to sleep without narcotic for that first awful week . I still have to take Advil pm to get through the night , something I do not need to do before ShakeWeight . I be real excite about this product ; I have high hope , and what a disappointment this be . plus I really hurt myself ! it be easy to get carry away with it , because it be fun to use , and I can see how the result could be amazing if only ... the manufacturer need to rethink the marketing of this product , bc the short instruction and the dvd be not very informative , they should stress that this device should be use along or as a part of a total exercise regimen , and that it be not mean to be the whole upper body workout . if you want to use this item you have to already be a gym rat , and be strong and in great shape , make it part of you regular workout routine ; also be a man would probably not be a bad thing -lrb- LOL -rrb- . so lady , if you be not a amazon -lrb- no pun intend , lol ! -rrb- or a body builder , start with the woman size , it be probably safer . let my pain be you warning ! I hope this can prevent other people from hurt themselves unnecessarily . I be in great shape before ShakeWeight , I certainly be not expect this injury to happen to I . it now be 7 week , and I still use the heating pad , and I can not sit at my computer for more than 20 minute at a time , or else I get a monster stiff neck -lrb- from the 5th vertebra to mid-back -rrb- . I wish I could sue they , for all this agony ; but they protect themselves against consumer suit with a little trademark phrase , in tiny letter somewhere on the box , but since I return it for a refund , I can not quote the phrase exactly , but it go something like this ; - consult you physician prior begin a new workout regimen - or something like that . as if ! most people do not go to the doctor until they really need to , when they be already hurt or sick ; not prior to start use a new fitness device , but I think if enough people get injure , it might raise the possibility of start a class action suit ... buyer beware