In postseason, VT1 and VT2 both occurred at similar V˙O2, watts, watts per kilogram, percent V˙O2max, %W V˙O2max, and %W max as in preseason. However, corresponding HR were lower postseason compared with preseason at both VT1 (134 ± 13 vs 141 ± 14 beats·min−1, P = 0.01; 69.6 ± 4.5% vs 73.6 ± 5.6% HRmax, P < 0.01) and VT2 (174 ± 10 vs 177 ± 11 beats·min−1, P = 0.03; 90.3 ± 1.7% vs 92.9 ± 3.0 HRmax, P = 0.01; Fig. 3). Mean sub-VT2 RER was greater preseason than postseason (0.94 ± 0.02 vs 0.92 ± 0.04, P = 0.01).
H was significantly greater postseason than preseason in SJ (47.4 ± 4.4 vs 44.7 ± 4.3 cm, P < 0.01) and CMJ (52.7 ± 4.6 vs 50.4 ± 5.0 cm, P < 0.01; Fig. 1). P max was not significantly different postseason compared with preseason, although it tended to increase in CMJ (P = 0.09).
Between preseason and postseason testing, skiers trained 1321 ± 249 min·wk−1. Weighted mean session RPE for all training sessions was 4.6 ± 0.8. Total training load was 9755 ± 3232 units. Athletes competed in 41 ± 7.6 races over the course of the season. Training distribution is presented in Table 3. Endurance training modalities included cycling, jogging, and team sports.
Compared with the cohorts of elite alpine skiers of similar age reviewed by Andersen and Montgomery (1), our subjects were as tall but were heavier and slightly leaner. This could indicate an increase in the physical requisites for success in this sport that has developed over the 18 yr between that report and our study. Similarly, our subjects displayed better explosive leg performance than an older cohort 7 yr earlier (5). Conversely, our subjects displayed lower aerobic capacities compared with peers in a more recent report (32).
The principal changes between preseason and postseason testing were increased V˙O2max, decreased HR corresponding to unchanged submaximal threshold W, and improved jump performance. Specific endurance training during the season (81 min·wk−1, 6.1% of total training), performed at low intensity (session RPE = 4 ± 0.16), was seemingly insufficient (15) to increase aerobic fitness. Moreover, such improvements in jump performance were not observed previously (5). Thus, the question arises about the reason for the manifested changes.
It is remarkable that aerobic capacity did not deteriorate despite several months of little specific endurance training (26). In moderately trained subjects, endurance exercise for 60 min·wk−1 did not prevent detraining of cardiovascular parameters (30). Thus, the primarily on-snow training and racing between preseason and postseason testing seems to have helped provide subjects' aerobic systems with an adequate stimulus for maintaining training adaptations.
Whereas an earlier publication (21) reported decreased V˙O2max over the course of a competitive alpine ski season, this may be less likely to occur in modernity. Changes in technique brought about by the advent of carving skis have increased the muscular effort required during turns because of greater centrifugal force (37). Accordingly, it seems that an increased energy demand leads to higher peak V˙O2 attained during ski runs with modern equipment (32,38). Namely, whereas earlier sources reported peak V˙O2 in top-level skiers during giant slalom (duration ∼80 s) of 80% V˙O2max (33,36), more recent reports confirm peak V˙O2 of 93% V˙O2max in giant slalom (32). Moreover, during shorter (45 s), more intense (∼200% W VO2max) slalom runs, high-level skiers achieve 80%-90% V˙O2max (38). Improvements in V˙O2max occur in relation to exercise time spent above ∼90% V˙O2max (14,23) yet can also be achieved by short (30 s) supramaximal interval training (23). Whether these principles apply to ski training should be further explored, although it seems from our results that the demands of modern technique may allow skiers to better maintain V˙O2max over the course of their competitive season, although specific endurance training is discontinued.
Although aerobic work capacity remained stable (preseason to postseason W VO2max, P > 0.05), there was in fact a significant increase in absolute and relative V˙O2max connected with a significant steepening of the V˙O2/W regression slope in postseason. Thus, additional circumstances seem to have influenced the skiers' metabolic response specifically. Although mere changes in glycogen availability can alter V˙O2/W by 100-200 mL·min−1 (6,29), we dismiss this explanation, considering the higher V˙O2max, similar BLamax and reduced submaximal HR we also observed in postseason (6,11,29).
One factor that conceivably affected V˙O2 response is the high-altitude training skiers performed during the summer and fall months. This period, which extended between 20 and 4 wk before pretesting, emulated a live low-train high model, where skiers trained intermittently (35-40 d, 15-20 h·wk−1 on average) atop a glacier at ∼3500 m altitude. Intermittent exposure to hypoxia at high altitude increases submaximal aerobic efficiency, manifest by a reduction in V˙O2 for a given submaximal W (19,28). Our ramp protocol did not afford V˙O2 steady states, which obscures inference regarding the true V˙O2 cost of exercise; submaximally, we saw a trend (P = 0.07) for reduced V˙O2 for slightly greater W at VT2. More similar to our results, Neya et al. (28) reported a decreased V˙O2/W relationship (regression from four submaximal steady states) after hypoxic exposure (11 h·d−1, 29 d). The lower O2 cost of energy production is the result of a shift from fat to carbohydrate oxidation (12). Concurrent with such alterations, V˙O2max may be unchanged (19,28) or reduced (13); in our subjects, V˙O2max was reduced in preseason. Our subjects do seem to have relied more heavily on carbohydrate oxidation in preseason compared with postseason on the basis of the slightly but significantly higher mean sub-VT2 RER we computed.
Any explanation of our results should also address submaximal HR responses. Strictly resulting from altitude exposure, submaximal HR have typically been lower in accord with reduced V˙O2 when measured in normoxia (19); in our subjects, HR were significantly higher despite slightly lower (nonsignificant) V˙O2 for equivalent W at VT1 and VT2 in preseason compared with postseason. Thus, an additional influencing factor we have considered is that a fatigued state due to an imbalance of training and recovery altered the results of performance testing in the preseason and that subjects were able to recover from this fatigue between test sessions. It has been hypothesized that HR at fixed submaximal W are increased in the presence of muscular fatigue owing to a reliance on additional motor units (9,22). This could feasibly have occurred in our subjects because recovery from muscular fatigue is perhaps the most fitting explanation for improved H in both SJ and CMJ over the course of a ski season, considering that no such improvement occurred elsewhere, even when specific jump training was performed (5).
Moreover, if muscular fatigue led to increased reliance on Type II muscle fibers for the same submaximal W, the altered fiber-type distribution in the used muscle mass could have slowed V˙O2 kinetics (2). Universal flattening of V˙O2/W slope, which we observed in preseason compared with postseason, also appears in hypoxia (31) or patients (17), where it is due to slower V˙O2 kinetics (31). The flattening expresses the inability of V˙O2 to adjust in pace with increasing work rate and concurs with reduced V˙O2max during ramp testing (17,31), which we also saw in preseason.
Although complete preseason training data were not collected in this post hoc study, retrospective analysis of two available athlete training logs (Table 4) indicates that the month before pretesting was characterized by fewer, longer sessions of greater and perceived intensity compared with the month before posttesting. Owing to seven additional high-intensity sessions in the month before pretesting, weekly training load was on average 7% greater. These two athletes trained and competed uniformly to their teammates and were also representative of the entire cohort in terms of seasonal changes in the dependent variables (Δ within 1 SD of group mean). Thus, training-induced fatigue could have altered HR and V˙O2 responses, as well as jump performance, in our subjects. Consequently, we hypothesize that V˙O2 kinetics or V˙O2/W slope could be of additional help for monitoring training tolerance and identifying excess fatigue in athletes. This possibility deserves further exploration.
A final noteworthy observation we made was an atypical relative flattening of the V˙O2/W slope beyond VT1 in both preseason and postseason testing. Typically, V˙O2/W slope in incremental exercise steepens after VT1 (2,16,24,31). Similarly to the V˙O2 slow component during constant work rate exercise, steepening occurs because additional fibers must be recruited (16). In contrast, we observed (to the same extent in preseason and postseason testing) reduced (P < 0.001) slopes above (preseason and postseason combined mean 8.75 mL O2·min−1·W−1) compared with below VT1 (10.11 mL O2·min−1·W−1), with lower V˙O2 at maximal W than would be predicted from sub-VT1 slope.
We believe this phenomenon to be the combined effect of our ramp protocol and the mediocre aerobic conditioning of the athletes we tested. In contrast to the aforementioned studies, where workload increase during incremental testing (ΔW) was about 25 W·min−1 (range = 10-35 W·min−1) (2,16,24,31), ΔW in our ramp protocol was 40 W·min−1 on average. In our subjects, VT1 occurred at a rather low relative intensity (preseason 40.3 ± 5.8% W max, postseason 38.5 ± 6.6% W max, P = 0.36), which indicates poor aerobic base fitness. Because the time constant of V˙O2 kinetics (τ) relates inversely to aerobic fitness and, moreover, to exercise intensity (20), we suppose that V˙O2 kinetics were too slow to keep up with the ramp protocol and that flattening emerged more dominantly at higher intensities, where ΔW/τ increasingly exceeded the protocol-defined ΔW/Δt. Also, it is feasible that the observed effect is statistically inflated because the sub-VT1 segments were so small (due to low %W max at VT1) in our subjects. Although many of our subjects possessed enough anaerobic reserve at the end of the ramp test to allow for a plateau in V˙O2, we recommend caution regarding implementation of quickly increasing ramp protocols for V˙O2max measures, unless subjects are highly trained (39). On the other hand, quickly ramping test formats may be especially helpful for evaluating changes in aerobic fitness or monitoring training tolerance, by V˙O2/W slope (kinetic response) analysis in addition to peak V˙O2 and W.
Although this study presents previously unreported seasonal changes in the physical characteristics of competitive alpine skiers, several limitations exist on its ability to identify the cause of these changes. Because it is a post hoc analysis of data we gathered for the purpose of monitoring these athletes' training, complete training records before pretesting, parameter data typical for diagnosing nonfunctional fatigue, and hematological data about high-altitude training are lacking.
In summary, we observed positive changes in V˙O2max, submaximal HR, and jump performance but unchanged aerobic work capacity between preseason and postseason in elite alpine skiers. Accordingly, whole V˙O2/W slope in ramp testing was significantly steeper in postseason compared with preseason, with a similar flattening beyond VT1 at both time points. We conclude that modern alpine skiing provides an ample cardiovascular training stimulus and that skiers are thus able maintain aerobic adaptations during their racing season. The complete causes for the changes we observed are uncertain; however, the possibility that V˙O2/W slope can be affected by a fatigued state because of incongruous preseason training should be further explored. Lastly, we concluded that ramp tests that increase W too quickly could be poorly suited for V˙O2max determination in untrained subjects but might provide additional information via slope analysis for monitoring both positive and negative responses to endurance training.
This study was supported by the Swiss Ski Federation. No funding was received from either the National Institutes of Health or the Howard Hughes Medical Institute. Results of the present study do not constitute endorsement by ACSM.
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Keywords:©2009The American College of Sports Medicine
V˙O2 KINETICS; SLOPE; ALTITUDE TRAINING; COUNTERMOVEMENT JUMP; SQUAT JUMP; RAMP TEST