Study: Strength Training Increases Bone Strength in Women

Geschatte leestijd: 8 minuten Women who engage in strength training develop stronger bones. By increasing bone strength in this way, the risk of the bone disease osteoporosis in old age is reduced. This is shown by research from the Norwegian University of Science and Technology that will soon be published in the Journal of Strength and Conditioning Research (1). Yet another reason for strength training for women!  

Osteoporosis

Osteoporosis is a progressive bone disease in which the mass and density of bones decrease (2). This increases the risk of bone fractures in old age. In women over fifty, there is a chance of as much as 50% of a bone fracture. In men over 50, this occurs in one in five cases (3). Due to the greater risk of bone fractures, much prevention research is focused mainly on women. Bone strength, bone mass, and bone density increase until about the age of thirty. After that, it only decreases. Maximum mass and density (“peak bone mass”) are reached somewhere between 20 and 30 years of age (4). Prevention of osteoporosis is therefore aimed at maximizing peak bone mass in young years and slowing the decrease in bone mass as age increases (5). Calcium and vitamin D are well-known ways to increase peak bone mass through diet, but training can also help. However, it is unclear which training method is most suitable for this purpose (6-8). Both strength training (high volume) and “plyometric high-impact training” have shown good results in this regard (8-10). “Plyometric high-impact training” involves explosive exercises where the high impact is provided by the body weight that must be absorbed with speed. Think of jumping rope and running, but also of ball sports such as basketball. The best results in previous studies came from a combination of both types of training (8,11,12).

Pelvis, Femur, and Spine

Common fractures due to osteoporosis include those of the wrist, shoulder, spine, hip, and femur. Especially a pelvic/femur fracture can lead to nasty complications. Analyses have shown that especially high-impact training contributes to increased bone density and mass, but this is largely limited to the femoral head (also called “femur head” or “hip head”) (6,8). The advantage of strength training is that it can be better targeted at the hip and spine (1).

Type of Training for Osteoporosis Prevention

Based on the above data, the influence of strength training and high-impact training, there is a suspicion that high acceleration during muscle contraction is important to stimulate osteogenesis, the formation of new bone tissue (13). Training for maximal strength differs from high-volume strength training in intensity and speed of execution. When training for maximal strength, heavier weights are used and fewer repetitions are done (often a maximum of 5). It is known that training for maximal strength increases explosiveness, or more precisely, the speed at which force is generated (14,15). This is called the Rate of Force Deployment (RFD). Moreover, training for maximal strength, not surprisingly, leads to more maximal strength (14,15). This maximal strength is expressed in the weight with which one can perform one repetition of an exercise, the so-called 1RM. The researchers at the Norwegian University of Science and Technology therefore suspected that both 1RM and RFD should be important components of a program aimed at preventing osteoporosis. Maximal strength training thus offers both of these components.

“Due to the special emphasis placed on progressive loading and rapid execution of muscle contraction, Maximal Strength Training is likely to promote higher strain rates in bone than conventional strength training, thus potentially exerting beneficial skeletal effects.” M.P. Mosti, Norwegian University of Science and Technology

“Hack Squat Best Exercise for Strengthening Hip and Spine”

The type of training was chosen; now it had to be decided which exercise(s) they would have their subjects perform. They chose the hack squat.

“Hack squat exercise, with loads resting on the shoulders, will provide compressive loading through the spine and the hip, both being sites that are particularly subjected to osteoporotic fractures. Thus, the hack squat exercise may be sufficient to induce beneficial effects at relevant skeletal sites. Based on this rationale, performing MST in a hack squat exercise may be an effective intervention for improving skeletal health. Hack squat MST may therefore provide a simple, low volume training method to increase bone mass in young adults.” M.P. Mosti, Norwegian University of Science and Technology

“Why Not Regular Squat?”

One may wonder why the researchers did not have the women do the regular squat (or “backsquat”). They did not explain this themselves. The regular squat is usually recommended because it makes the stabilizing muscles of the pelvis and spine work harder. This results in a stronger “core” and reduces the risk of injury. I am also not aware of any data showing that the hack squat causes more or less compression of the spine. Therefore, I can only imagine that they chose this because the machine in which the hack squat is performed is likely safer for inexperienced women than the regular, free squat, especially when training with such heavy weights that only five repetitions can be done. Another reason may be that the regular squat is technically difficult. Increases in strength can then be caused relatively more quickly by improved coordination from the brain than by muscle adaptation itself. This can make it more difficult for the research to correctly evaluate the data.

The Study Setup for Strength Training to Prevent Osteoporosis

The Norwegian researchers divided 30 healthy women aged 18 to 30 into a test group and a control group. Two weeks after testing to establish the baseline (how strong they were at the start), training began. The test group trained for 12 weeks, three times a week. After a warm-up, they did four sets of 3 to 5 repetitions at 85%-90% 1RM, so 85-90 percent of the weight with which they could do one repetition. They were instructed to perform the concentric phase (in this case during leg extension) as explosively as possible. Additionally, they were encouraged to train to failure, meaning they should push themselves to the limit. As soon as they could do more than 5 repetitions, the weight was increased by 2.5 kilos to ensure progressive resistance. The control group trained according to a training protocol for osteoporosis prevention established by the American College of Sports Medicine (5). This consists of a combination of the previously mentioned high volume strength training (less weight, more repetitions) and high-impact training such as jogging, stair climbing, volleyball, or basketball, etc.

Results

Explosive strength almost doubled in the test group, peak power increased by almost 13%. In the control group, this was an increase of 27% and almost 6%, respectively. A significant difference:

“The TG improved dynamic RFD and PF by 81.7% (p < 0.01) and 12.6% (p < 0.001), respectively. The CG also increased dynamic RFD and PF by 27.2 ±% (p = 0.031) and 5.8% (p < 0.01), respectively. However, dynamic RFD and PF improvements were greater in the TG compared with the CG”* M.P. Mosti, Norwegian University of Science and Technology

*TG=Test Group, RFD=Rate of Force Deployment, PF=Peak Force, CG=Control Group. Regarding bone density and mass, the differences were also clear. It is probably clear that these are smaller differences. A doubling of bone mass, for example, would be quite problematic. The bone density of the bones is expressed in density and the amount of minerals, called Bone Mineral Density (BMD) and Bone Mineral Content (BMC). In the test group, the BMD and BMC of the spine increased by 2.2% and 3.4%, respectively, while there was no increase in the control group. The BMD and BMC of the hip both increased by 1% in the test group, while there was also no increase in the control group.

Considerations Regarding the Study

Bones are not static. Bone mass is continuously renewing in a process called “Bone Remodeling Period” (16). Bone mass is reduced by cells that can absorb bone tissue (osteoclasts) and increased by cells that deposit bone tissue (osteoblasts). The “Bone Remodeling Period” is the cycle that osteoclasts and osteoblasts together need to do their work (17). The duration of this period is 3-6 months for humans (19). The study may have lasted just long enough for one cycle, but it may have been too short. Absorption and release of bone tissue by osteoclasts and -blasts do not have to run synchronously. It is possible that more bone tissue was deposited than absorbed in the meantime, resulting in a temporary increase in bone mass. If the results of a study are viewed at such a moment, they may show a distorted picture. Furthermore, the population is very small. Only 30 people were included in the study, half of whom served as controls. The researchers therefore suggest that longer-lasting research should be conducted among more people to verify the current findings.

Conclusion of Research

Aside from these caveats, the conclusion is clear:

“Squat-exercise MST may be used as a simple and effective strategy for optimizing peak bone mass in young adults, and thereby contribute to prevent age-related bone loss and osteoporotic fractures.” M.P. Mosti, Norwegian University of Science and Technology

It’s noticeable that the hack squat isn’t specifically mentioned. Therefore, I would recommend doing the regular squat. If you don’t have experience with this, I would first suggest learning it with high volume strength training, using lighter weights and more repetitions to get the correct execution down.

Elastic Bands for Greater Increase in Rate of Force Deployment

Recently, I described in an article that performing squats with an elastic band as additional resistance likely increases the RFD/explosive strength more. If Rate of Force Deployment is so important for the effect on bones, then you would think that training with weights and elastic bands would have an even greater effect on the bones. I therefore put this to the (lead) researcher, M.P. Mosti, from whom I received a response yesterday. He indicates that they are aware that there are multiple methods to increase RFD, and elastic bands are indeed likely one of them. They chose not to use such methods for the research to more easily establish a relationship between increased 1RM and RFD. Moreover, they were primarily focused on specifically loading specific bones, which seems easiest with free weights. He does “absolutely agree that combining various exercises known to improve physical performance (such as elastic bands for RFD) would be relevant.” He hopes that future research will demonstrate the added value of these methods.

What’s the Use of This Knowledge?

Will women now start mass-scale maximal strength training? No, it would already be a win if more women recognize the benefits of “normal” strength training (less weight, more repetitions). By benefits, I mean primarily the benefits for their appearance; Better fat burning and curves where they want them. If that’s not reason enough for women to engage in regular strength training, they will have even more difficulty with maximal strength training, which is still seen as more “hardcore men’s training.” Especially if they should do this to prevent a leg fracture 20 to 40 years later. Therefore, I simply see it as yet another advantage in the list that speaks in favor of strength training for women, whether it’s maximal strength training or high volume training.

References

1. Mosti, M.P.; Carlsen, T.; Aas, E.; Hoff, J.; Stunes, A.K.; Syversen, U. Maximal strength training improves bone mineral density and neuromuscular performance in young adult women. Journal of Strength & Conditioning Research: POST ACCEPTANCE, 14 April 2014 doi: 10.1519/JSC.0000000000000493
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