573 workers from a national public administrative authority in Denmark were cluster randomized into one of 5 groups:
1) Supervised training for 1 hour per week;
2) Supervised training for 20 minutes, 3 times per week;
3) Supervised training for 7 minutes, 9 times per week;
4) Supervised only during first week, 20 minutes, 3 times per week;
5) Reference group – no training.
All intervention groups performed the same exercises using dumbbells, starting with a warm-up of 10 repetitions of each exercise (approximately 50% of 1RM). The exercises were initially performed at a load of approximately 20RM and progress to 8RM over the weeks. The training program included: front raise, lateral raise, reverse flies, shoulder shrugs and wrist extension.
Following the intervention period, a total of 344 participants (60%) completed the follow-up questionnaires.