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The aim of this study was to monitor the long-term effects of skiing on health-related parameters and implant related factors like loosening and wear in patients with total knee arthroplasty. This paper describes the overall study design, general demographics, and physiological demand of the intervention phase. A control group design consisting of an intervention group (n = 14; age: 70.4 ± 4.5 years) and a control group (n = 17; age: 71.5 ± 5.1 years) was utilized in this study. Parameters of interest were measured during pre-, post-, and retention test sessions. During the 12 weeks of intervention, an average of 25.5 days of guided skiing was conducted by each patient. Daily heart rate (HR) profiles and global positioning system data throughout the ski day were recorded. The intervention group completed an average of 3393 vertical meters of downhill skiing, with a total skiing distance of 33.6 km/day. Average skiing speed was 8.2 m/s. In the skiing phase, the average physiological load was 75.9 ± 6.6% of HRmax . Further effects of the 12-week skiing intervention on the tested parameters will be reported in the following papers of this supplementum.

This study investigated the effect of a 12-week recreational skiing intervention on lower limb muscle strength and cardiorespiratory fitness in participants with unilateral total knee arthroplasty (TKA). Twenty-seven older adults (70 ± 5 years) were assigned to the intervention (n = 13) or control group (n = 14) after surgery (2.5 ± 1 years). Leg muscle strength was measured using an IsoMed 2000 dynamometer and cardiorespiratory fitness was determined by cycle ergometry before and after the intervention as well as after an 8-week retention period. The skiing intervention led to increased muscle strength in the operated leg during unilateral single joint isometric extension (maximal force: 11%; P < 0.05; rate of torque development: 24%; P < 0.05) and during the unilateral multi-joint isokinetic single leg strength test (8%; P < 0.05). This resulted in a decreased asymmetry index in the isokinetic test (13% to 5%; P < 0.05). These adaptations remained unchanged toward the retention test. No effect was observed for cardiorespiratory fitness. The results demonstrate that muscle contraction forces required during recreational skiing in individuals with TKA seem adequate and effective to increase quadriceps and hamstrings muscle strength in the initially weaker operated leg and to reduce an augmented post-operative asymmetry index.

This study investigated the effectiveness of recreational skiing as an intervention to improve quadriceps muscle architecture, strength, and antagonistic co-activation in patients with unilateral total knee arthroplasty (TKA). Hence, patients with TKA were assigned to either an intervention group (IG) or control group (CG). The IG completed a 12-week guided skiing program whereas the CG was instructed not to change their daily routines for the same period and was not allowed to ski. Before, after the intervention/after an 8-week retention period m. rectus femoris (RF) cross-sectional area (CSA), m. vastus lateralis muscle thickness, fascicle length, and pennation angle were measured with ultrasonography, while isometric (90° knee angle) knee extension, flexion torque and m. biceps femoris co-activation were assessed on an isokinetic dynamometer in 26 patients. There were significant and stable increases in RF CSA for the operated (10%; P < 0.05) and non-operated leg (12%; P < 0.01) after the training period in the IG whereas no changes were observed for the CG (all P > 0.05). There were no significant effects for other parameters (all P > 0.05). Overall, the skiing intervention was successful in increasing muscle mass in TKA older patients.

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