Is there any information on the use of weighted vests during exercise? One of my group fitness instructors is wearing a weighted vest when she works out. I am not aware of any special athletic event that she is training for. I think she feels it "burns more calories." Do you have any research on the use of weighted vests?
As with any training tool, both the benefits and costs must be considered before use. This means you need to look objectively at not only the publicized benefits (often flouted by companies who make a profit selling them) but the “other” side of the equation.
So with that in mind, I will tackle this question from several directions.
As a Physical Training Instructor/Personal Trainer
Physiologically, increasing the weight the body must move increases the energy required to perform a given task. For example, at the extremities, increases in shoe weight by 100g causes an increase in VO2 requirement by up to one percent.
In terms of load around the body, like from a weighted vest, Pandolf devised an equation that inputs a person’s fitness level with his body weight and speed of movement to estimate a given workload with an added external weight. Although this equation is mostly associated with load carriage (and hence has strong military/police/fire department applications), it is useful in having a look at the impact of additional weight on a person’s VO2 levels.
I will use two generic examples:
- Male A = 80kg with a VO2 of 48.7 ml/kg/min-1 (2.4 km time of 10:40 or a Shuttle Run time of Level 10.6 – Australian male average 20-29 years old)
- Female A = 65kg with a VO2 of 37.5 ml/kg/min-1 (2.4 km time of 14:10 or a Shuttle Run of Level 7.4 – Australian female average 20-29 years old)
For Male A, with the heavier body weight and higher VO2, an increase in weight from 0kg to 2.5kg equals an increase in VO2 workload by around 0.6 percent and increases to 2.1 percent for a five kg load. Sustainment time drops by four percent for the first 2.5kg and then by another 10 percent for the additional 2.5kg.
For Female A, the increase in weight by 2.5kg equals an increased VO2 of around one percent and a decrease in sustainment time of around 7.5 percent. An increase in external load to five kg equals an increase in VO2 by just over two percent and a decrease in the maximum amount of time you could sustain the activity by around 15 percent.
So ultimately, increasing external load leads to an increase of work effort, which equals increased energy utilization. With this in mind, however, there is only so much work a person can perform. So if a person is fit and performing at optimal levels metabolically, increasing load will not make much difference to the energy output, although it will alter other performance areas, as other parameters will have to adjust (i.e., running 400m with and without a weight vest at maximal effort). While both are maximal, you would not be able to run the weighted 400m in the same time.
As a Conditioning Coach
>Speed/power resisted training utilizes aids that allow specific sports movements to be completed under resistance slightly greater than that expected for normal performance. Swimming tethered to a bucket or cycling dragging another cyclist are two examples. However, it must be remembered that the resistance must be applied to the direction of acceleration, so while a vest may be useful in more vertical applications (like jumping), it would be of less value for horizontal applications (like sprinting) that would be better suited by other tools like wind sails/parachutes.
As a Physiotherapist
My first concern would be skeletal impact. While many claims are made about how good loading and weighed vests are for increasing bone density, they painfully neglect the other end of the equation, which is the ability of the body to respond to the bone loading.
Wolff’s law has bone adapting to loads imposed on them by altering the distribution and amount of mass of the bone. Therefore, an increased load will increase bone mass. This is, however, on the provision that the body can respond. Think of why distance runners get stress fractures. They are loading the bones, but the body cannot repair and adapt at the rate required. Thus, if the body cannot adapt to the additional skeletal impact of moving, jumping and running with a weight vest, bone health will deteriorate rather than improve. Likewise, those with osteopenia or osteoporosis need to be extremely cautious that any skeletal impact is not excessive and beyond the ability of the skeletal structure to respond. Just before you think you are in the clear, remember that osteopenia or osteoporosis is not limited to the older population or the less fit. Amenorrhoeic women with poor dietary intakes of calcium (two components of the Female Athlete Triad - see "related articles" at right) are also at risk. The increased load on the joint must also be considered, especially if the client is suffering from any joint disease or deterioration.
In terms of the often flouted “core conditioning,” I would be very skeptical as to wether training with a vest would have any impact on true “core conditioning.” Firstly, in optimal conditions, the core muscles will contract prior to voluntary contractions. It is only when there is a dysfunction that the muscles fire with the voluntary contraction or later, or not at all. Physiotherapists/Physical Therapists use exercises to aid in the retraining of inhibited core muscles. These exercises utilize sub maximal contractions to ensure that the local muscles contract without over activation/stimulation of the global muscles. Therefore, if a client’s local muscle control systems are not working correctly, a weighted vest (just like the plank or prone hold exercise) will not improve core control and will in fact facilitate poor neural programming.
Finally, from an injury prevention point of view, the vest is inert weight and not living tissue with receptors. This means that if you miss-step, your proprioceptive systems have to work harder and overcome greater inertia to prevent you from having an injury. When muscles and the nervous system fatigue (i.e., towards the end of a group exercise class), the muscles may simply not be able to respond to a higher work demand (either in contractile strength or speed or both in combination) to protect the musculo-skeletal system.
When wearing a weighted vest, there is also the issue of thoracic impendence. For the average person, the resistance to breathing will only be slight but for those with exercise induced asthma, respiratory concerns or training to a very high level of fatigue, I would urge caution. I would likewise ensure that the load is light and that the vest has a “quick release” that the CLIENT can reach. For COPD patients (or similar) with piston breathing patterns, I would strongly advise against a weighted vest.
Some final points to consider if training a client with a weighted vest:
- Progression: Make sure that a very gradual loading program is designed with structured periods of de-loading to allow the musculoskeletal systems time to adapt to the training stimulus.
- Fit and bruising: Make sure that the vest fits well, otherwise bruises and chaffing will ensue.
- Poor dynamic posture: Watch for changes in dynamic posture caused by a weighted vest. Changes to spinal posture, acromioclavicular depression and forward head postures are some key postural shifts.
- Monitor closely for early injury signs: For example, acromioclavicular depression from a heavily weighted vest has the potential to cause supraspinatus impingements by decreasing space in the supraspinatus outlet.
So in a nutshell, I hardly ever use a weighted vest with clients as I can find other ways to increase metabolic demand without the additional concerns noted above. With this in mind, though, I do use the vests frequently when training clients to improve their relative strength (i.e., chin ups, dips etc) as a key benefit of the vests is the distribution of load around the body rather than at one point.
I have also used the weighted vest with several power based athletes (i.e., acrobats, gymnasts, divers) prior to competitions. I have them wear the vest for a short period prior to the warm up for psychological reasons mostly (although the benefit is based on a neurological response), whereby they feel lighter going into the event with the vest removed.