Purpose: The main aim of the present study was to investigate the effects of a workplace exercise intervention on physical functioning. Dose of the exercise and other physical activity outside the intervention were controlled for. The other aims were to determine the physical strain of training and determine training force as a percentage of work time (OPA), leisure time (LTPA) and time spent on all activities (AT). Methods: The study was a cluster randomized controlled trial (CRT) with each

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... artment as the unit of randomization (n=36, n=19, n=15, n=25). The cross-over design consisted of one 15-week intervention period of resistance training (30% 1RM) and training guidance, and another period of the same length with no training or guidance. The subjects (n=90) were office workers [mean age 45.7 (SD 8.5) years]. Percentage body fat was measured using bioelectrical impedance, spinal flexibility with goniometer and a cervical measurement system, muscular strength with a 5RM test and a hand grip test. Subjective physical condition was assessed by questionnaire and physical activity by questionnaire and diary. The statistical analysis was based on linear mixed models. Results: The active component of the intervention, light resistance training, significantly increased both subjective physical condition (p=0.015) and upper extremity extension strength (p= 0.001). Intervention had no effect on percentage body fat, spinal flexibility, hand grip strength or lower extremity strength. The estimated increase in subjective physical condition during the 15-week period was 4 units (95% CI 1-7) or 6% and in upper extremity extension strength 1.3 kg (95% CI 0.5-2.1) or 4%. Relative physical strain, measured as percentage of maximal oxygen consumption, was 33.7%. Training force was 1.12 metabolic equivalent hours per week, representing 2.0% OPA, 5.9% of LTPA and 1.2% of AT. Conclusion: Light resistance training during the working day had a positive effect on the office workerss ubjective physical condition and strength of upper extremities. Controlling for training dose and other physical activity outside the intervention and confounding factors provides for a better specificity and understanding of the dose-response and effectiveness of exercise intervention on physical functioning among office workers.