Fig. 2

Schematic overview of the study protocol, including its time line (A; ^‡indicates the defined baseline measurement for the specific outcome measure), training volumes during the resistance training (RT) intervention (B), perceived exertion (Borg RPE, 6–20) reported after training sessions (C), and relative training loads (% of 1RM) during the training period (D). Training volume is presented as average increases in per-session for lower-body appendices from the first week of training (kg ^. repetitions; high-load (10RM) and low-load (30RM) leg press and knee extension combined). Training loads in numeric values (kg) during the resistance training intervention are provided in Additional file 1: Fig. S1. COPD, participants diagnosed with chronic obstructive pulmonary disease; Healthy, healthy control participants; *statistical different from 1th training week; ^#statistical difference between COPD and Healthy. Data are presented as means with 95% confidence limits. Methodological notes on retrieval of outcome measures: i) Lung function. Spirometry testing was performed following the guidelines from the American Thoracic Society and the European Respiratory Society [72]. Participants with COPD were tested before and after inhalation of two bronchodilators (salbutamol/ipratropiumbromid). ii) Muscle strength and performance (STR and Musc. perf). Muscle strength was assessed as one-repetition maximum (1RM) in unilateral knee extension and leg press, bilateral chest press, and handgrip. Muscle performance was defined as the number of repetitions achieved at 50% of pre-study 1RM and was assessed using unilateral knee extension and bilateral chest press. Isokinetic unilateral knee-extension torque was tested at three angular speeds (60°, 120° and 240°^. sec⁻¹; Humac Norm, CSMi, Stoughton, MA, USA). iii) One-legged cycling and bicycling performance (1-LC and VO₂max). Participants conducted one-legged cycling tests (Excalibur Sport, Lode BV, Groningen, the Netherlands) to assess O₂-costs and mechanical efficiency [73] during submaximal cycling, and maximal one-legged oxygen consumption (V̇O₂max) and maximal workload. Maximal two-legged cycling V̇O₂max and workload were tested on a separate day. Oxygen consumption was measured using the JAEGER Oxycon Pro™ system (Carefusion GmbH, Höchberg, Germany). iv) Functional performance (Func.). Functional tests were conducted as the maximal number of sit-to-stands during one minute (seat height: 45 cm) and as the number of steps onto a 20 cm step box during 6 min. v) Health-related quality of life (SF-36 and CAT). All participants completed the Short Form (36-item) Health Survey (SF-36). COPD participants also completed the COPD Assessment Test (CAT) questionnaire. vi) Muscle thickness and body mass composition (US/DXA). Muscle thickness of m. vastus lateralis and m. rectus femoris were measured using B-mode ultrasonography (SmartUs EXT-1 M, Telemed, Vilnius, Lithuania). Body mass composition was measured using dual-energy X-ray absorptiometry (DXA; Lunar Prodigy, GE Healthcare, Madison, WI, USA). At pre study, all participants completed a questionnaire regarding regular weekly activity habits. The results (time spent for different activities) were translated into energy expenditure (kcals^.week⁻¹) during activities using number of metabolic equivalents provided in Jetté et al. [74]. During week 11, all participants conducted a dietary registration, in which they logged their dietary intake for three days, including one weekend day