The primary purpose of the present study was to compare physiological and perceptual responses to maximal and submaximal exercise between upper-, lower-, and whole-body exercise modes in elite crosscountry (XC) skiers. Twelve elite XC skiers performed 5-7 submaximal 5-min stages and an incremental test to exhaustion using upper-body poling (UP), running (RUN) and diagonal roller skiing (DIA), randomized on three separate days. Here, power output, cardiorespiratory variables, heart rate (HR), blood lactate concentration (BLa) and rating of perceived exertion (RPE) were determined. Peak power output increased gradually from UP to RUN and DIA, whereas peak oxygen uptake (VO2peak), peak HR, O2pulse and total RPE were clearly lower in UP than RUN and DIA (P<0.05). At submaximal workloads matched for either RPE, %HR or BLa, the main pattern was that BLa was higher and VO2 and HR lower in UP compared to RUN and DIA (P<0.05). DIA showed ~10% and 35% higher VO2 than RUN and UP at RPE 10-13, and had lower muscular RPE values than UP and RUN at a given % of peak HR (P<0.05). Most of the differences in cardiorespiratory variables between modes were eliminated when they were normalized to VO2peak or peak HR in the respective mode. Due to the low power production in UP, endurance training in this mode exhibits too low values of VO2 to tax the cardiovascular system sufficiently. In RUN and DIA, the similar VO2peak values indicate that both modes can be effectively used during high-intensity training and to determine VO2max in elite XC skiers. However, the relatively high VO2 values at low perceptual stress with submaximal DIA indicate that the large amount of power produced when combining upper-and lower-body work exhibits high oxidative flux even during low intensity training. Overall, these findings should be taken into account when athletes and coaches are monitoring and prescribing training in future approaches, in particular in sports where athletes varies between training with upper-, lower-and whole-body exercise modes.

Rationale The main purposes of this study were to compare mitochondrial respiration in M. triceps brachii and M. vastus lateralis between elite cross-country (XC) skiers and physically active controls (CON), and to explore the associations between mitochondrial respiration in these muscles and peak oxygen uptake ( O 2peak ) in arm- and leg-dominant exercise modes. Methods Thirteen male elite XC skiers (age: 25 ± 4; peak oxygen uptake ( O 2peak ): 75.5 ± 4.2 mL⋅kg -1 ⋅min -1 ) and twelve CON (age: 26 ± 3; O 2peak : 57.2 ± 6.4 mL⋅kg -1 ⋅min -1 ) had microbiopsies taken from M. vastus lateralis and M. triceps brachii, which were analyzed for various measures of mitochondrial respiration using high-resolution respirometry. Thereafter, all participants tested O 2peak in both running (RUN) and upper body poling (UBP). Results XC skiers had generally higher mitochondrial respiration in M. triceps brachii compared to CON ( P < 0.001), whereas no significant group-differences in mitochondrial respiration in M. vastus lateralis were revealed. XC skiers had higher mitochondrial respiration in M. triceps brachii compared to M. vastus lateralis ( P = 0.005–0.058), whereas in CON, most mitochondrial respiration measures were higher in M. vastus lateralis than in M. triceps brachii ( P < 0.01). When all athletes were pooled, there was a strong positive correlation between O 2peak in UBP and mitochondrial respiration in M. triceps brachii on several measures ( P < 0.01), whereas no correlation was found for RUN. Conclusion The higher mitochondrial respiration found in M. triceps brachii compared to M. vastus lateralis among our elite XC skiers demonstrates the potential for the arm muscles to adapt to aerobic endurance training. The opposite pattern found in CON, clearly showed lower mitochondrial respiration in M. triceps brachii compared to XC skiers, whereas respiration in M. vastus lateralis did not differ between groups. The strong positive correlation between mitochondrial respiration in M. triceps brachii and O 2peak in UBP indicate that arm muscles’ respiratory function may be a limiting factor for O 2peak in arm-dominant exercise modes.