Physical Activity as Intervention Against Age-related Loss of Muscle Mass and Function

Retirement has been recognized as a critical turning point in determining physical activity behaviours in old age. The literature gives a varying picture regarding change in physical activity level with work retirement but often a reduction in total physical activity has been reported. Retirement typically takes place at a time where the skeletal muscle mass, -strength and -power declines by 1-3% per year.

Interventions to promote physical activity in adults aged 55 to 70 years have been shown to be effective at 12 months but it is very unclear if the effect is maintained thereafter. Both exercise at home or at a center improves health and physical function - but home based programs appear to be superior to center based programs in terms of adherence to exercise especially in the long-term.

In older adults, strength training at 60% of 1RM has been shown to be sufficient for large effect on muscle function and muscle protein synthesis, and potentially lower loads (45-60% 1RM) have effect when adding more repetitions.

The overall objective of the study is to assess the long-term effects of 12 month of supervised high-intensity center based resistance training or "guided" moderate-intensity home-based resistance training relative to a non-exercising control group upon muscle power, -strength and -mass, physical function, physical activity level and health in older people around the time of retirement.

The hypotheses are:

• Supervised high-intensity center based resistance training over one year results in the best improvement in muscle power and bodily function
• "Guided" moderate-intensity home-based resistance training will result in a more active lifestyle and thus in sustained elevated activity level after the 1-year intervention period. Thus in the long run (several years) "guided" moderate-intensity home-based resistance training has superior effects compared to supervised high-intensity center based resistance training upon functional ability, health and potentially also cognitive function.

450 participants recruited through advertisements in local newspapers will be included in this three-armed, single-blinded randomized trial. After baseline assessment they will be randomized to one year of 1) supervised, high-intensity progressive, resistance training conducted in machines three times weekly in a local fitness center 2) "guided" moderate-intensity home-based resistance training conducted with elastic bands and body weight three times weekly. "Guided" means that the participants are offered supervised resistance training once weekly in addition to home based resistance training 2 times weekly or 3) various social and cultural activities that do not require physical activity.

All participants complete a wide range of tests before and after the 12 months intervention period and the primary time point for outcome assessment will be at 12 month. The same "test battery" is conducted in the subsequent years (2, 4, 7, and 10 years later) as a follow-up.

Inclusion criteria

• Independently living men and women
• Between 62 and 70 years

Exclusion criteria

• Subjects dependent on help/nursing etc.
• Severe chronic obstructive pulmonary disease, cardiac arrhythmias or known decreased left ventricular ejection fraction, non-treated hyper/hypothyroidism, dementia, active cancer.
• Surgical diseases: Bone, muscle, tendon or joint injuries compromising participation in exercise regimens.
• Implanted magnetic devices incompatible with MRi-scanning.
• >1 hour of exercise weekly, except light activities such as stretching/gymnastics and bike-riding/walking as transportation.