Friday, August 19, 2011

All shook up: Does the Shake weight device really work? by Jerry Brainum

 You've probably seen those ubiquitous infomercials touting an exercise device called the Shake Weight. My first impression when viewing this device is that it's a training aid for female porno actresses. But that's not what it's actually designed for. The Shake Weight (SW) is shaped like a dumbbell, and is available in a 2.5 pound version for women, and a 5-pound version for men (at least for men who read Men's Health regularly). You grip the SW with one or both hands, and vigorously shake the weight back and forth. Springs on both ends of the SW permit the weight to move back and forth, producing a resistance that the purveyor of the device calls "dynamic inertia."  Other claims for the device are that it's far more effective compared to free weights in building muscle definition, size, and strength  in far less time compared to standard weight workouts. This is based on the claims that using the device causes muscle to contract 240 times per minute.
     The SW has been the subject of many humorous remarks and skepticism. But the salient question here is: does it actually work as advertised? A new study tested the device, comparing it to basic free weight exercises. The study subjects were 16 healthy adults, average age, 21. They completed two exercise trials: one with the SW, the other with a free weight dumbbell of the same weight. As such, the women in the study used a 2.5 pound dumbbell, while the men used a 5 pound dumbbell. The SW part of the study involved four exercises: one-handed biceps shake; two-handed triceps shake; one-handed shoulder shake;, and the two-handed chest shake. The free weight dumbbell exercises used for comparison were: biceps curl;triceps extension;shoulder press; and chest fly. For each exercise, surface electromyograph leads were placed on the working muscles to determine the extent of muscle involvement
     The results showed that EMG values were higher for all muscles tested during the Shake Weight compared to the dumbbell exercises. But when comparing specific muscle activity for each exercise, the SW did not always result in greater EMG activity. When doing the biceps curls, muscle activity for the biceps wasn't greater when doing SW compared to DB curls. The middle or lateral deltoid was not activated more in the SW shoulder press compared to the DB press, and the pectoralis muscle wasn't more activated when doing the SW compared to the DB fly exercise.
      The researchers also noticed that the triceps was more active then the targeted muscle for most of the SW exercises. Thus, when doing the biceps curls, the triceps showed higher muscle activity than did the biceps when using the SW device. The same held true for the chest flys; triceps showed higher activity then the pecs when using the SW. The study authors think that a strong triceps contraction is required to control the motion of the SW. This explains the initial finding of higher EMG values for the SW. But when applied to specific muscles, the SW showed no superiority at all.
      In a second part of the study, the study authors determined how much weight you would have to lift to equal the muscle stimulation provided by the SW. This was found to be 48% of one rep-maximum. Since the average one-rep max for the women in the study when doing curls was 20.5 pounds, they would need to lift a 10-pound dumbell to get muscle stimulation equal to that of the SW device.
      The researchers who conducted this study noted that the muscle stimulation provided by the SW appears to be similar to that of isometric muscle contractions, in which the muscle contracts strongly without any movement. This is in contrast to the typical eccentric and concentric muscle contractions that occur with free weights.Since isometric muscle contractions only strengthen muscles in one isolated position, the value of the SW  for functional strength benefits is questionable at best. Not even for porno actresses.
Porcari J, et al. Does the Shake Weight live up to its hype? J Sports Sci Med 2011;10:598-99.

©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.

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