High Intensity Strength Training & Bone Mineral Density in Young Women
Condition: Osteoporosis
MeSH terms: Osteoporosis
Study type: Interventional

Summary: 
      The current guidelines emphasize the prevention of bone loss, by building up bone mass in
      young age, as one of the most important measures to reduce the incidence of osteoporosis.
      Strength training and "explosive" exercises have been shown to have beneficial effects on
      bone mass and bone metabolism in both young and postmenopausal women. However, meta-analysis
      concludes that it is still unclear what type of exercises, intensity and execution that is
      most effective for skeletal adaptations. The following study will examine the effect of 12
      weeks of heavy, explosive strength training on bone mineral density and bone metabolism in
      young, healthy girls aged 18-30 years.
    

Detailed description: 
      Background:

      Osteoporosis is a progressive, systemic skeletal disorder characterized by low bone mineral
      density (BMD), and deterioration of the microarchitecture of bone tissue, with a consequent
      increase in bone fragility and susceptibility to fracture. Typically the disease shows no
      symptoms until a fracture occurs, hence referred to as the "silent epidemic". In Norway one
      of two women and one of four men experience a fragility fracture after the age of 50. The
      loss of bone strength with age likely reflects the skeletal response to hormonal changes and
      the mechanical environment with decreased physical activity. Osteoporotic fractures often
      happen as a consequence of minimal injury, especially at the hip, spine and wrist. Hip
      fracture is associated with excess mortality during the first year after fracture ranging
      from 8.4% to 36%. The increased mortality risk may persist for several years thereafter,
      highlighting the need for interventions to reduce this risk. Osteoporosis is a common disease
      and recognized as a global problem by the WHO.

      The American College of Sport Medicine suggests exercise as a countermeasure against bone
      loss in postmenopausal woman and elderly subjects. Peak bone mass is thought to be attained
      by the end of the third decade, hence the early adult years might be the final opportunity
      for its augmentation. It is indicated that optimizing peak bone mass may have long-term
      effect on bone health. Intervention studies with young women show that high impact exercises
      may improve BMD in young adults. High intensity strength training also seems to effectively
      improve BMD and the ratio of bone turnover markers. Furthermore, an explosive execution of
      movement may be important for obtaining BMD improvements from resistance training. Maximal
      strength training (MST) is characterized by high mobilization of force, high loads, and few
      repetitions (3-5 reps.) per set with emphasis on maximal force mobilization in the concentric
      part of the movement. Recent studies have shown that MST is highly efficient for improving
      maximal strength (1RM) and rate of force development (RFD). Parameters such as 1RM and RFD
      are closely related to BMD. In addition, a recent study from our group showed that 12 weeks
      of MST training (three times each week) improved bone mass in the hip and spine of
      postmenopausal women, diagnosed with osteoporosis (article in preparation). In the present
      study we want to investigate the impact of heavy, explosive strength training on bone mass
      and bone metabolism in young and healthy woman which have not yet reached peak bone mass.

      Physical activity and BMD:

      One of the main factors responsible for the high incidence of osteoporosis is physical
      inactivity. Several studies have shown that physical activity can lead to an increase in BMD.
      Resistance- and impact exercises have shown to be most effective. A number of studies
      performed with sedentary young women performing high impact training has shown significant
      improvement in BMD at the femoral neck and lumbar spine. A study with postmenopausal women
      showed that power training is more effective in maintaining BMD in the lumbar spine and total
      hip than conventional strength training.

      The effect of training at the cellular and tissue level can be divided into 3 main factors:

        -  Increased osteoblast activity and bone formation

        -  Reduced osteoclast activity and bone resorption

        -  Increased stability of the bone's architectural structure

      In terms of prevention of osteoporosis the current exercise guidelines, according to the WHO,
      is encouragement of a physically active lifestyle. Weight bearing activities, preferably
      resistance training are recommended for patients with osteoporosis. Peak bone mass is an
      important factor in determining long-term fracture risk. Therefore, effective strategies to
      maximize peak bone mass in young adults are essential. Evidence indicates that resistance and
      high-impact exercise are the most beneficial to maintain and optimize peak bone mass in young
      adults. However, studies investigating such exercises are not altogether conclusive, and the
      mode of exercise, regarding type of exercise, intensity and execution, still remains unclear.
      Since MST exercise may increase bone mass in osteoporotic women, and improves 1RM and RFD
      (which are closely related to skeletal health) we wish to investigate the potential of MST
      training to increase bone mass and improve bone metabolism in young female adults, who have
      not yet reached peak bone mass.

      Goals of the study:

        1. Investigate the effect of heavy, explosive strength training on bone mineral density
           compared to a control group in young, healthy women over a period of 3 months.

        2. Study the effect of this training intervention on bone formation and resorption markers

        3. Study the effect on physical capacity measurements.
    

Intervention name(s): Heavy, explosive strength training; recommendations
Intervention type(s): Behavioral; Behavioral
Intervention description(s): All participants of the training group will pursue a 12 weeks of heavy, explosive strength training, 3 sessions a week for a total of 36 sessions. The training session will include one squat exercise only, which allows muscle contraction of the quadriceps from a 90° bend at the knees to straight legs.; The control group will be encouraged to follow a training program according to recommended exercise guidelines:
Weight bearing activities (walking, jogging or strength training)
30 - 60 minutes, 3 - 5 times each week
A total of 2 - 3 hours each week should be achieved
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: Exercise; osteoporosis; prevention