Physical activity is a potent way of relieving some of the adverse morbidities associated with COPD, such as muscle atrophy and reduced muscle quality. It is thus problematic that 20-30% of patients fail to elicit positive adaptations to training. This oddity has been ascribed inherent muscular properties, with potential links to comorbidities such as vitamin D and testosterone deficiency and the nature of the training program. In the present project, a double-blinded RCT will be performed to disclose the functional and biological efficacy of vitamin D supplementation (with concomitant ingestion of 1000 mg Ca2+) on the outcomes of 10 wks strength training in 100 aging individuals with or without COPD. The strength training intervention will be preceded by 3 weeks of progressive introduction to training protocols.

50 COPD patients and 50 healthy subjects will be allocated into two strata and separately randomized into two equally sized supplementation groups; (1) vitamin D3 and (2) placebo. The planned 50:50 ratio between COPD patients and healthy individuals may change, depending on the access to COPD patients. All subjects will perform lower-limb strength-training protocols in a contralateral manner: (leg 1) high-resistance (10 RM) and (leg 2) low-resistance (30 RM). Such a one-limb-at-a-time protocol ensures training that is unconfined by the cardiorespiratory limitations inherent to these patients, and allow comparison of the two training modalities in a manner unconfined by individual variation in exercise adaptability. A pilot study investigating the possible central pulmonary capacity limitation to two-legged strength training exercise in COPD patients will be performed. In this pilot study, we will compare exercise performance involving large and small muscle mass. In addition, all subjects will perform a selection of bilateral upper body exercises (10 RM), ensuring adequate hormonal responses and compliance to the study. The study is likely to revitalize guidelines for rehabilitation of COPD patients, and to provide vital information regarding the role of vitamin D in adaptations to strength training.

For outcome measures specific to COPD pasients, final analyses will be performed on data from the COPD population only. For other outcome measures, final analyses will be performed on data merged from COPD patients and healthy subjects. An important rationale behind implementing healthy control subjects is to increase the statistical power of outcome measures unrelated to COPD epidemiology, which are of general relevance to physiological adaptation to strength training. In a related set of analyses, we will perform between-groups comparisons, including multivariate analyses. We will also compare the efficacy of high- and low-resistance strength training in COPD patients and healthy control subjects. The two training modalities are expected to result in similar muscular adaptations.

In general, baseline vitamin D levels in blood, measured as 25(OH)D, is anticipated to be a determinant of the efficacy of the strength training intervention. In response to vitamin D3 supplementation, individuals with low baseline levels of 25(OH)D are expected to display more pronounced changes in biological active vitamin D, leading to more pronounced changes in functional and biological outcome measures in response to strength training. In contrast, supplementation may not lead to further elevation of blood 25(OH)D levels in individuals with high baseline levels, essentially meaning that vitamin D3 ingestion will be leveled out by or exceeded by the elimination of vitamin D derivatives. In these individuals, vitamin D3 ingestion will not have an additive effect on functional and biological outcome measures in response to strength training. To assess individual variation in vitamin D responses, data on functional and biological variables will be divided into quartiles based on baseline 25(OH)D-levels, whereupon comparisons will be made between low-end and high-end quartiles. Individual variation in responses to vitamin D supplementation and strength training will also be assessed using a mixed model approach.