Does the Shake Weight(®) live up to its hype?

Muscular strength is an important component of physical fitness and can be improved by using free weights (i.e. barbells, dumbbells), weight machines, elastic bands, or body weight exercises (Stone et al., 2000). A new product in the exercise marketplace which is advertised to increase strength is the Shake Weight ®. The Shake Weight ® is a dumbbell shaped fitness device, sold by Fitness IQ (Vista, California). There is a 2.5 lb (1.13 kg) version for women and a 5 lb (2.27 kg) version for men. While gripping the Shake Weight ® with one or both hands, users vigorously shake the weight back and forth. Springs on both ends allow the weight to move back and forth, creating a resistance which the manufacturer calls " dynamic inertia ". The Shake Weight ® claims to build definition, size, and strength in less time than traditional weights, with the muscle purportedly contracting up to 240 times per minute (www.shakeweight.com). The purpose of this study was to determine the degree of muscle activation when using the Shake Weight ® compared to traditional dumbbell exercises.5 kg) completed two exercise trials, one with the Shake Weight ® , the other with an equal weight dumbbell. Females used the 2.5 lb (1.13 kg) Shake Weight ® and a 2.5 lb (1.13 kg) dumbbell; males the 5 lb (2.27 kg) Shake Weight ® and a 5 lb (2.27 kg) dumb-bell. The Shake Weight ® trial consisted of four exercises: one-handed biceps shake, two-handed triceps shake, one-handed shoulder shake, and two-handed chest shake. The following dumbbell exercises were used for comparison: biceps curl, triceps extension, shoulder press, and chest fly. During each exercise surface electromyography (EMG) was measured from the biceps brachii, triceps brachii, middle deltoid, and pectoralis major, on the right side of the body. The average EMG for each exercise trial, for each muscle, was " normalized " by dividing by the maximal EMG value recorded during a previously recorded MVIC trial. The averaged EMG from each exercise trial was represented as a percentage of MVIC for each specific muscle. The % MVIC values during the four Shake Weight ® exercises versus the dumbbell exercises are illustrated in Figures 1 through 4, respectively. EMG was higher for all of the muscles tested during the Shake Weight ® compared to the dumbbell exercises. However, when comparing specific muscles for each exercise, the Shake Weight ® did not always …