A Systematic Review of the Effects of Strength and Power Training on Performance in Cross-Country Skiers

To identify and evaluate current scientific literature concerning the effect of strength, power and speed training on relevant phys-iological and biomechanical characteristics and performance of competitive cross-country skiers (XCS), the databases Scopus and PubMed were searched systematically for original articles in peer-reviewed journals. Of the 599 studies retrieved, 12 met the inclusion criteria (i.e., assessment of outcome measures with rel-evance for XCS performance; involvement of traditional re-sistance training; application of external resistance to the body; intervention longer than 4 weeks; randomized controlled trial). The methodological rigor of each study was assessed using the PEDro scale, which were mostly poor-to-fair, with good method-ological quality in only two articles. All of the strength/power/speed interventions improved 1RM (0.8 -6.8 ES), but findings with respect to jump performance, ability to generate force rapidly and body composition were mixed. Interventions demonstrated moderate-to-high ES on XCS specific performance compared with control (mean ES = 0.56), but the pattern observed was not consistent. None of the interventions changed anaerobic capacity, while in most studies VO2max was either unchanged or increased. Work economy or efficiency was enhanced by most of the interventions. In conclusion, present research indicates that strength training improves general strength, with moderate effects on XCS performance, and inconclusive effects on work economy and VO2max/VO2peak. Strength training with high loads, explosive strength training, or sprint interval training seem to be promising tools for modern XCS training. Future investigations should in-clude long-term (e.g., >6 months) strength training to allow suf-ficient time for increased strength and speed to influence actual XCS performance. Moreover, they should include both sexes, as well as upper-and lower-body muscles (trained separately and together) and employ free weights and core training. Methodo-logical differences and limitations highlighted here may explain discrepancies in findings and should be taken into consideration in future research in this area.