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Maintaining bone mineral density in postmenopausal women through resistance training

One of the consequences of aging process of the human body is to be accompanied by sedentarity and thus, a loss of muscle mass (i.e., sarcopenia) and a decrease in bone mineral density. These phenomena appear without distinction in men and women. However, for the postmenopausal woman, the decrease in bone mineral density can often lead to osteoporosis. Osteoporosis is a significant loss of bone mass that weakens the skeleton and increases the risk of fractures (e.g., frequent fracture of the femoral neck in older women).

It is now well established that physical activity and exercise are conducive to muscle and bone gain. And in the case of the elderly, the exercise helps maintain, and even increase, muscle mass (see our article) and bone mineral density despite the effects of aging. Scientific research has shown that bone mineral density is strongly associated with activities where high impacts and load bearing are common and those where muscle tension is high.

The strength of the stress on the bone, the rate at which this stress is applied, its frequency and its distribution are all parameters that affect the bone mineral density. Nevertheless, which parameter is most important during a workout is not yet quite clear.

The Study

In 2005, a team of German researchers investigated the effect of speed of execution in weight training in two groups of postmenopausal women to study the influence of the speed at which a constraint is applied to the skeleton. For this, 53 postmenopausal women participated in the study. All these women had already had the opportunity to participate in a similar study 3 years ago.

Training protocol :

The duration of the study was 12 months. The participants were divided into 2 training groups with a specific protocol for each group : a "Strength" group (n = 28) and a "Power" group (n = 25). The weekly training program for both groups was as follows :

• Two sessions of resistance training (about 60 min / session) : The session consisted of a warm-up of 20 minutes, then exercises performed on machines allowing the work of the main muscle groups of the body. The protocol alternated 12 weeks at high intensity (70-90% of 1RM) and 5 weeks at low intensity (50% of 1RM). The difference in protocol between the two groups was based solely on the speed of execution of the concentric phase of the exercises performed :
  • "Strength" group : 4s for the concentric phase and 4s for the eccentric phase
  • "Power" group : Fast / Explosive for the concentric phase and 4s for the eccentric phase
• 1 gymnastic session (about 60 min / session) : The aim of these sessions was to improve coordination, flexibility and endurance.
• 1 session at home (about 25 min / session): This session consisted of skipping rope, stretching, isometric exercises and exercises with elastic bands.

NOTE : After 6 months of training, 18 women from the "Strength" group and 16 women from the "Power" group were tested on a horizontal leg press. The test consisted in executing 6 repetitions at 75% of the 1RM while respecting the speed of execution specific to each group. A force plate was placed under the feet to measure the force developed over time. From these measurements, the researchers determined the relative force produced (ie, the percentage ratio between the average of the 6 maxima and the displaced load), the magnitude of this force (ie, the ratio in percentage between the average of the differences between maximum and minimum on each repetition and the displaced load) and the rate of force development (ie, the amount of force developed per second) (see Table 1).

Supplements :

Each participant received calcium and vitamin D supplements throughout the study for a daily total of 1500 mg Calcium and 500 IU Vitamin D. All diets were controlled and adapted to each woman.

Before-after measures :

Each participant was tested at the beginning of the study and 12 months later. The tests included :

• Anthropometry :
  • Height
  • Body mass
  • Fat mass
  • Lean mass
  • Quantity of water in the body
• Measurement of bone densitometry at the level of the lumbar vertebrae, the upper femur and the wrist.
• Maximal isometric force
• Questionnaire on pain during training

Results & Analyzes

The researchers compared the results of the two groups to see the influence of the two types of training on bone mineral density. Of the 53 participants, 11 were excluded from the treatment of the results, either for lack of regularity in training (< 2 / weeks), or because of injuries or illnesses. Measurements before the start of the study showed that there was no difference between the two groups at all levels.

Regarding the effects of training on BMD parameters, women in the "Power" group performed better than those in the "Strength" group at the lumbar vertebrae and at the femur level. In fact, while the mineral density of the "Power" group was maintained throughout the study at the level of the lumbar vertebrae and the femur, the mineral density of the "Strength" group decreased significantly on these two sites. As seen in Table 1, the difference in speed of execution during the concentric phase of the movement made it possible to play on different mechanical parameters at the same time (relative strength developed, relative amplitude, and rate of development). However, which of these parameters is the most important is not yet clearly defined.

Training with high concentric speed allows maintenance of bone mineral density in postmenopausal women. Nevertheless, training of this type, even with the use of machines, can be problematic in the elderly, since training with a high rate of contraction induces greater stresses in the tendons and joints. To investigate this possibility, researchers had administered questionnaires on perceived pain. The intensity and frequency of the pains were not different from one group to another. After 1 year, there was even a tendency to decrease pain in major joints in both groups. The alternation of 12 intense weeks and 5 more moderate weeks also helped reduce muscle and nervous fatigue and improved recovery. It should nevertheless be noted that these women had already participated in a study of this type 3 years ago and that they were in a certain way better prepared for resistance training.

Practical Applications

The results of this study are encouraging as they demonstrate that it is possible to slow the adverse effects of age and hormonal changes with an appropriate training mode. However, it is problematic to set up training with high speeds in people who are not used to physical activity. Nevertheless, the questionnaires on pain showed that after 1 year of training, the pain decreased for the "Power" group.

A gradual and adapted implementation of machine-based weight training exercises would enable postmenopausal women and the elderly to combat the effects of aging and improve their physical fitness while minimizing the pain that can be caused by training.

References

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