The Shake Weight has two versions, a 2.5 lb weight (advertised for women) and a 5 lb. weight (advertised for men). It is said to "shape and tone" women's arms, shoulders and chest, while the men's version will help them get "strong, toned, and ripped arms and chest." The video below discusses how to use The Shake Weight:
So, as you see above, the resistance glides back and forth, requiring frequent contraction of opposing muscles to keep the movement going. Its recommended use is six minutes per day, every day. At first, I thought the product was created so infomercials about it could be made for the entertainment of teenage boys, but The Shake Weight has actually been a huge hit, achieving over $40 million in sales! The question is: How useful is The Shake Weight as a workout method?
The Shake Weight: A Scientific Breakdown
As you read this assessment, keep in mind that I'm not concerned with whether or not it can make someone sweat, get out of breath, or get the heart racing. I'm concerned with characteristics of exercise that produce actual long-term improvement:
- Positive and Negative Resistance: While targeting the biceps and triceps in one exercise seems efficient, it means one major component is missing: the negative (otherwise known as the eccentric part of a rep, when muscles work to decrease the speed at which the weight goes down). Basically, The Shake Weight features a positive contraction for the biceps in one direction, and a positive contraction for the triceps in the other direction. This is similar to how muscles work in a pool or without gravity. Unfortunately, the negative phase is critical to causing the microscopic tears that eventually lead to muscle growth, so an exercise without it is limited in providing hypertrophy.
- Range of Motion (ROM): The elbow joint can experience about 150 degrees of movement. Ideally, an exercise for the biceps and triceps would utilize most of that distance. The Shake Weight, as you can see in the video, puts the elbow through about 20 degrees of motion. This minimal ROM presents two problems. First, decreasing ROM means less muscle fiber involvement. In plain terms, if you use less of the available muscle, you will see less change. The second problem has to do with strength development. Exercises will only produce strength gains in the parts of the movement that they're used in. The Shake Weight will only make a person stronger in about one-seventh of the possible distance that the elbow moves in. Strength in the rest of the movement will not be affected.
- Progression: Every successful workout has a system of progression. A solid progression system forces continual and positive physiological adaptations. My clients either lift more weight (even if it's just a 1/2 lb. more) or the same weight with the intent of going for more reps/time. The Shake Weight does actually have a few ways to progress its workout: switch to the heavier version (if started on the 2.5 lb. dumbbell), go for more time, straightening the arms more during the workout, and switching from both arms to just one. I don't think that all of these are quality progression tactics (discussed in the intensity section), but The Shake Weight does have a system of progression, so I will give it credit for that.
- Intensity: Intensity is key when it comes to producing gains from strength training. While The Shake Weight may produce a heart-pumping workout, any exercise that can be performed or six minutes is not intense-enough to produce much hypertrophy, if any. The fact that it can be done for six minutes means that this workout mostly uses aerobic metabolism and aerobic muscle fibers. Exercises that predominantly use the fast twitch fibers, which have the largest capacity for growth, lead to complete fatigue in less than two minutes (I.E. heavy weight lifting and sprinting).
- Muscle Groups Involved: Even if all of the previous factors favored The Shake Weight, there's one major problem with it: only the biceps, triceps, forearms, pecs, and deltoids are used. That leaves all of the back, hips, legs, and abs with nothing. Muscles hypertrophy the most when all are being exercised, so even those in the arms and chest will not experience the full growth possible due to the lack of other large muscle stimulation. The Shake Weights come with DVDs for full body workouts to do in addition to the regular Shake Weight workout, but there goes the claim that you have to exercise just six minutes per day.
While the commercials are certainly entertaining and the simplicity of using one product and one single exercise sound appealing, The Shake Weight has major flaws in the absence of negative resistance, a minimal range of motion, a lack of intensity, and the absence of a workout for most of the major muscle groups. Also, when terms like "tone" and "sculpt" are used, they are speaking about fat loss as much as muscle development, and fat loss is mainly due to improvements in the diet (specifically, removing foods from your diet). Infomercials rarely display effective workout products, and The Shake Weight is no exception.