Lactate accumulation in skeletal muscle occurs at exercise intensities above the anaerobic threshold. The metabolic production of lactate anions occurs when the rate of pyruvate production by glycolysis exceeds the rate of its decarboxylation and use for oxidative phosphorylation in the mitochondria (6). The conversion of pyruvate to lactate by lactate dehydrogenase allows glycolysis to continue at a high rate as the reaction reduces Nicotinamide adenine dinucleotide (NADH) to NAD+, replenishing the pool of NAD+ for use in the glycolysis (6,19). As lactate is a strong anion, its accumulation in skeletal muscle results in a decrease in pH in the intramuscular environment as electroneutrality is maintained by the dissociation of H2O into H+ and OH− (14). Consequently, muscle acidosis occurs, impairing contraction kinetics of the muscle fiber and ultimately performance of the muscle (1,6). Accumulation of by-products of anaerobic metabolism in the muscle, including lactate, hydrogen protons, and inorganic phosphate, has also been suggested to activate group III and IV afferent receptors, resulting in reduced excitatory capacity of the alpha motor neuron pool of the muscle, impairing muscle activation and motor control (6,13,19). Therefore, the clearance of these metabolites is expected to reduce peripheral neuromuscular fatigue and has positive effects on muscle function.
Active recovery uses lower intensity aerobic exercise after high-intensity exercise to promote clearance of waste products to facilitate recovery or can be performed between bouts of high-intensity exercise to improve performance on subsequent exercise repeats (2,8,14,16). Sustained activity below the anaerobic threshold influences lactic acid removal from type II skeletal muscle fibers by maintaining perfusion of these fatigued muscle fibers while increasing aerobic metabolic rate of oxidative muscle fibers (2). Thus, blood flow to support removal from highly anaerobic muscle fibers producing lactic acid occurs while simultaneously enhancing the usage of lactate by other oxidative tissues, ultimately promoting the clearance of lactic acid from the muscle (6,17).
The removal of lactic acid from intramuscular spaces into the blood occurs via monocarboxylate transporters (MCT) (4). The cotransport of a lactate anion and a proton from intramuscular spaces into the blood and to other tissues for oxidation is influenced by the concentration gradient from the muscle to the blood (7,25). The population of MCTs in skeletal muscle can be increased by high-intensity training, allowing a greater flux of lactic acid from the muscle (10,24). Skeletal muscle perfusion and uptake/oxidation in other tissues (i.e., heart, liver, and type I oxidative muscle fibers) maintain a favorable gradient between the muscle and the blood by promoting clearance of lactate from the blood.
Alpine skiing is a high-intensity intermittent sport that requires both supramaximal (above
) metabolic energy production (27) and force production (3). Technical events, slalom and giant slalom (GS), have shorter radius turns, faster angular velocities, and higher metabolic costs compared with the faster longer radius turns of the speed events, super giant slalom (super G) and downhill. Electromyographic studies in elite GS and super G skiers (3,5) have shown the hip and knee extensor and flexor muscles to produce forces near or above laboratory-measured maximum voluntary isometric force. The predominance of slow velocity and high-force contractions of muscles activated during alpine skiing result in high intramuscular pressures and reduced muscle perfusion and oxygen delivery/waste removal (5,22,23). Further challenges to oxygen delivery to and removal of waste products from these muscles may be influenced by environmental factors. Alpine ski training and racing often occur at very cold ambient temperatures, which may also contribute to limiting muscle perfusion (9). Furthermore, high altitude (2,000–5,000 m above sea level) and acute hypoxia are possible, resulting in greater production of lactate for a given submaximal workload (26). Although studies have shown a paradoxical reduced lactate response independent of O2 consumption—termed the “lactate paradox”—this phenomenon does not typically occur for weeks with acclimatization (26), much longer than the typical alpine ski training camp or competition. Reduced arterial O2 saturation after GS and slalom training runs has also been reported (23).
Supporting high-energy demands for a 1- to 2-minute training course, with muscle perfusion and oxygen saturation potentially compromised by environmental influences, results in an exaggerated reliance of alpine skiers on anaerobic energy production. In highly trained ski racers, metabolic demand has been reported to be 160–200%
measured in GS and slalom, respectively (27), with an estimated 65% of energy being derived from anaerobic sources in technical events. Consequently, the high metabolic demands combined with the physiological limitations in removal result in high production and accumulation of lactate, measured in the blood after an alpine ski run. Blood lactate has been observed to be 10–14 mmol·L−1 in a single GS and slalom run, respectively (20,27).
As a given training block for highly trained alpine ski racers is between 6 and 10 bouts (training runs) depending on training volume, the ability to clear lactic acid from the muscle is important for delaying peripheral fatigue and maintaining performance. The training environment of alpine ski racers presents unique challenges logistically for recovery between training runs, as training courses may be in variable terrain and remote from areas that could accommodate traditional recovery equipment (i.e., stationary bike). The importance of active recovery between training runs for promoting blood lactate clearance and delaying fatigue in alpine skiing has yet to be identified. Therefore, we sought to examine the effects of low-intensity aerobic active recovery between training runs on blood lactate clearance and fatigue in a training session with highly trained alpine ski racers. We hypothesize that active recovery will result in lower blood lactate concentrations and that this will correspond with improved training run times and lower incomplete training runs compared with static recovery.
Experimental Approach to the Problem
We used highly trained alpine ski racers in a randomized controlled trial to investigate the effects of on-hill active recovery performed between training runs on blood lactate clearance and fatigue. The skiers were randomized to either an active recovery, comprised of a 3-minute walk with ski poles, or a static recovery control group who remained stationary in their skis. Each group performed a volume of runs typical of a training session in training courses adhering to International Ski Federation (FIS) regulations but with low technical demand to support maximum completion of training runs. To determine the effect of on-hill active recovery, changes in blood lactate concentration were measured at the top and bottom of each run, whereas fatigue was measured by time to complete training runs, rate of incompletions, and ratings of fatigue.
Fourteen subjects, actively competing on men's (n = 7; age, 18.0 ± 1.1 years; 83.1 ± 7.1 kg; 184.3 ± 4.8 cm) and women's (n = 7; age, 18.5 ± 1.5 years; 63.8 ± 4.2 kg; 166.4 ± 3.6 cm) Nor-Am and National Collegiate Athletic Association circuits, participated in the study. Average FIS point profiles were 42.9 ± 17.4 FIS points in slalom for women and 41.6 ± 10.6 FIS points in GS for men. Average international rankings were 626 ± 440 in slalom for women and 1,023 ± 435 in GS for men. Participants gave informed consent, and all study protocols were approved by the research ethics board of the University of Toronto.
The study was performed on the first day of an 8-day on-snow training camp at the Timberline snowfield in Mount Hood, Oregon. The testing was conducted at 2,600 m above sea level on a run with an approximately 35% gradient. Each training lane was treated with 8 bags of urea fertilizer salt, commonly used to maintain a hard consistent snow surface. Participants arrived at the ski hill at 0730 hours for baseline measures and then proceeded to the training lane for standardized on-hill warm-up consisting of 2 runs of moderate-intensity free skiing and 1 run of course inspection. The men's training course (n = 7) was a 25-gate GS with a 26.5-m radius (distance from one gate to the next). The women's training course (n = 7) was a 45-gate slalom with a 9-m radius. Each participant performed 8 runs in their respective training course and performed their randomly assigned between-run recovery protocol, either active (ACT) or static (CON) recovery, at the top of the training course before each run. Blood lactate and perceived fatigue were measured immediately before they started their run at the top of the course and within 2 minutes of completing their run at the bottom of the course. Time to complete the run and rate of incomplete runs were also recorded. The chairlift ride was 6 minutes in duration such that, performing their training run with a 3-minute recovery intervention, testing at the top and bottom took 12 minutes.
Participants were randomly assigned to either ACT or CON recovery with equal men and women in each group. The ACT condition walked along the road at the top of the training course with their skis off for 3 minutes using their poles to engage their arms at a slow to moderate pace (250 m in 3 minutes). The CON condition remained stationary in their skis at the top of the course for 3 minutes. After their recovery intervention, they had top of course measurements taken and then commenced their training run.
Blood Lactate Measurements
Blood lactate concentration was measured from a finger prick sample using a LactatePro portable blood lactate analyzer (Arkray, Kyoto, Japan). Fingers were cleaned with an alcohol swab, the fingertip was lanced, and the first blood droplet was wiped clear, allowing an uncontaminated sample from the second blood droplet. Blood lactate samples were acquired immediately before the participants' training run and within 2 minutes of completing their training run. Samples were taken at baseline, at the top of runs 1, 2, 5, 6, and 8, and at the bottom of runs 1, 2, 5, and 8.
Perception of Fatigue
Fatigue was rated on a 10-point Likert scale that ranged from 1, “Debilitated,” to 10, “Fully recovered”; thus, a lower rating indicates higher fatigue. The participants were asked to rate their perception of fatigue before having their blood lactate measured at baseline and at the top and bottom of runs 1, 2, 5, 6, and 8. Participants were familiarized with the scale in a laboratory visit a week before the training camp.
In addition to the skiers' perceptions of fatigue, the time to complete a run was recorded for the men in the GS course using a Brower Bib ID XS (Brower, Draper, Utah, USA), wireless timing system. Training run time started when the skiers skied through the start wand at the top of the course and ended when the skiers crossed the infrared beam placed 10 m vertically from the last gate. Performance changes were normalized by comparing runs 2 through 7 with the time to complete run 1 to account for interindividual differences in speed. Did not finish (DNF) rates were recorded for all participants.
All data were analyzed using a 2-condition by 6-time point (training run number) analysis of variance with repeated measures. All values are expressed as mean ± SD. The assumption of sphericity was tested with Mauchley's W. In the event that Mauchley's W was significant, a Greenhouse-Geisser correction was used. Post hoc analysis of significant main and interaction effects were analyzed using Tukey's least significant difference. The alpha value was set to 0.05.
Blood Lactate Concentration—Top of the Course
A significant time effect for blood lactate concentration at the top of the run was observed (F (5,25) = 17.968, p < 0.01). Post hoc analysis showed significant increase in blood lactate concentration from baseline at runs 5 (4.9 ± 1.0 mmol·L−1), 6 (6.9 ± 1.1 mmol·L−1), and 8 (5.8 ± 0.8 mmol·L−1) for CON, whereas blood lactate concentrations in ACT did not significantly increase from baseline. No significant main effect for condition was observed, although a trend was observed, p = 0.68. A significant interaction effect was observed for condition and time point (F (5,25) = 5.868, p = 0.001). Blood lactate concentration was significantly greater in the CON group compared with the ACT group at runs 5 (4.9 ± 1.0 and 3.3 ± 0.5 mmol·L−1, respectively), 6 (6.9 ± 1.1 and 3.4 ± 0.6 mmol·L−1, respectively), and 8 (5.8 ± 0.8 and 2.7 ± 0.4 mmol·L−1, respectively) (Figure 1).
Blood Lactate Concentration—Bottom of the Course
A significant time effect for blood lactate concentration measured at the bottom of the run was observed for both conditions (F (5,25) = 17.346, p < 0.001). Blood lactate concentration was significantly elevated from baseline. The greatest increase in blood lactate concentration was observed at runs 5 and 6 for both ACT and CON. A significant interaction effect was observed for condition and time point (F (5,25) = 5.839, p < 0.01). Blood lactate concentration was significantly greater in the CON group compared with the ACT group at runs 2 (6.1 ± 0.8 and 3.9 ± 0.3 mmol·L−1, respectively) and 6 (6.2 ± 0.9 and 4.8 ± 0.4 mmol·L−1, respectively) (Figure 2).
Perceptions of Fatigue
A significant time effect was observed for perception of fatigue in both ACT and CON groups (F (5,25) = 41.166, p < 0.001). The greatest ratings of fatigue were observed at runs 6 and 8 in both ACT and CON groups. No significant differences were observed between baseline perceptions of fatigue between groups (Figure 3).
A significant time effect was observed in the CON group (p ≤ 0.05) for time to complete a training run compared with time to complete run 1, whereas no significant time effect was observed in the ACT group. The CON group had significantly longer run times (slower runs) in runs 5 and 6 compared with run 1 (0.81 ± 0.8 and 1.3 ± 1.2 seconds, respectively), and no male participant in the CON group completed run 7 or 8. The ACT group was associated with significantly shorter run times (faster runs) in run 6 compared with the CON group (0.18 ± 1.0 compared with 1.3 ± 1.2 seconds). Did not finish rates were recorded for all participants. Eleven DNFs (incomplete runs) were recorded in the CON group, of which 8 were in the last 2 runs, compared with 0 DNFs in the ACT group (Figure 4).
The aim of the study was to determine the effects of active recovery performed between training runs on blood lactate clearance and subsequent effect on performance and perceptions of fatigue in alpine ski racers. Fourteen provincial and collegiate level alpine ski racers underwent active (ACT) or static (CON) recovery at the top of a training course between each of 8 training runs of either GS or slalom training. The intensity of the training runs was reflective of that typically experienced during a training session of competitive alpine ski racers. In accordance with our hypotheses, the novel findings of this study were that 3 minutes of on-hill active recovery performed at the top of a training run resulted in significantly lower blood lactate concentration than static recovery, which has never before been reported in alpine skiers. Although lower blood lactate was not associated with reduced perceptions of fatigue, it was associated with faster training run times and higher training run completion rates, which has also not been previously reported.
We used blood lactate measured from a finger prick sample immediately before and 1–2 minutes after training runs in alpine ski racers as a measure of metabolic stress. All participants experienced a significant increase in blood lactate concentration from the top to the bottom of each training run for the first 6 of 8 runs. The average increases in blood lactate observed were 4 mmol·L−1 (ACT) and 6 mmol·L−1 (CON), with a maximum increase of 6.9 mmol·L−1 observed at the bottom of run 5 in the CON group. Veicsteinas et al. (27) observed blood lactate concentrations of 11.7 ± 2.7 mmol·L−1 in slalom training and 12.4 ± 1.9 mmol·L−1 in GS, measured in Italian National team athletes. The higher values observed in the study by Veicsteinas et al. (27) is likely because of either differences in study population as they used Italian National team athletes or course length (∼20 seconds longer). Interestingly, significant differences in blood lactate concentration were observed between groups at the bottom of run 1 despite no significant differences at the top of run 1. An active warm-up before intense dynamic exercise has been previously shown to attenuate the accumulation of blood lactate during cycle ergometry exercise (8). This may be attributed to the increase in aerobic energy pathway upregulation achieved during the initial bout of active recovery performed before run 1 in the ACT group, reducing their reliance on anaerobic energy production and consequently lactate production in run 1.
The observation that ACT resulted in significantly lower blood lactate concentrations measured at the top of the course of runs 5, 6, and 8 compared with CON is not surprising. Many other studies implementing active recovery between high-intensity bouts of exercise in other activity types have been shown. Martin et al. (15) found active recovery (80 rpm cycling at 40%
on a cycle ergometer) to be more effective than massage therapy or rest at promoting blood lactate clearance when used between 3 sets of Wingate maximal anaerobic tests. High-intensity alpine skiing has been shown to impose energy demands greater than
(27), maximal to supramaximal contractile force (3), and a high reliance on anaerobic metabolism (20,27). A major challenge in studying the physiological demands of alpine skiing is the difficulty of replicating motor patterns and physiological demands in a laboratory. Unique contractile profiles, in which the eccentric loads predominate compared with isometric or concentric loads, because of the effect of gravity (3,18) make it hard to replicate and difficult to compare with other high-intensity intermittent activity. Thus, although the metabolic demands of a Wingate test and an alpine ski training run in a highly trained skier may be similar, the recruitment patterns and contraction velocity would be considerably different. Nevertheless, considering that alpine ski training is performed at supramaximal intensities with a high anaerobic contribution and subsequent increase in by-products and associated peripheral fatigue, the agreement of observation that active recovery is effective at promoting lactate clearance is reasonable.
By the final training run in the session, the CON group showed reduced blood lactate concentrations at the bottom compared with the top of the training run. This may be because of the negative effect of lactic acid on anaerobic energy production in the muscles or a shift in muscle fiber recruitment toward more oxidative muscle fibers. Kröll et al. (12) observed a shift of predominantly type IIa fiber recruitment in vastus lateralis to type I fibers as the muscle fatigued. Reduced lactate production from early to later runs was also observed by Seifert et al. (21); however, this study used recreational skiers and lower intensity skiing. An alternative explanation to the reduction in blood lactate concentration is the reduced finish rate observed in the CON group. A total of 8 incomplete runs were recorded in the CON group in the last 2 runs compared with 0 in the ACT group.
Although the ACT group was associated with lower blood lactate concentration, faster run times, and fewer incidents of incomplete runs, these did not correspond with reduced perceptions of fatigue. Perceived fatigue increased from runs 1 to 8 with no differences between experimental groups at the top or bottom of any training run. It may be that rating of perceived fatigue is more indicative of central fatigue, and the peripheral fatigue that may be associated with lactic acid accumulation is not reflected in this measure. This is supported by the slower performance on training run time and greater number of incomplete training runs that were observed in the CON group compared with the ACT group. This is important for ski racers as the time to complete a run is the singular performance variable measured in races. Furthermore, high speeds and forces experienced during training can result in serious injury, and this risk increases with fatigue. Studies have shown that the accumulation of anaerobic metabolic by-products, including lactate and muscle acidosis, results in stimulation of group III and IV afferent receptors, impairing muscle activation and motor control (11,28). A study inducing blood flow occlusion during recovery resulted in stimulation of these afferent receptors 3 minutes post-fatiguing handgrip exercise, whereas they returned to baseline in the nonocclusion group. Stimulation of these afferents has been reported to negatively affect motor control (11), suggesting significant implications for a highly technical sport with extremely high speeds and forces, such as alpine skiing. Given the high intramuscular pressures associated with alpine skiing (22) and subsequent restriction in blood flow (23), paired with the high anaerobic costs (27), the restoration of blood flow and associated clearance of metabolites implicated in peripheral fatigue are paramount to the ability of the skier to perform technically and safely. The greater rate of incomplete runs observed in the CON group may be indicative of increased peripheral fatigue not reflected by the subjective fatigue rating.
The aim of this study was to assess the effect of active recovery on blood lactate concentrations and fatigue in alpine ski racers to provide them with meaningful results to apply in their race training. As such, an emphasis was placed on external validity of the study, resulting in some logistical limitations, which we wish to address. Both men and women were used; as the aim of the study was relevant for both groups and for adequate sample size, both groups were required. The groups skied different disciplines requiring different energy and muscle performance demands; however, slalom and GS are technical events and have been shown to result in similar increases in blood lactate concentration (27). Additionally, because of equipment malfunction, no objective measure of performance (i.e., run speed) was recorded for the female participants skiing slalom, resulting in incomplete data sets that could not be accurately analyzed with statistics. We used subjective ratings of perceived fatigue, time to complete a training run (in the males' skiing GS only), and rate of run incompletion as indicators of performance implications associated with changes in blood lactate concentration.
Despite the high anaerobic demands of alpine skiing and compound challenges to aerobic energy production induced by environmental factors, the use of on-hill active recovery strategies requiring no equipment for clearing lactate has not been studied previously in this population. Our findings show that on-hill active recovery performed between training runs in alpine ski racers is effective at facilitating lactate clearance from the blood. The group performing active recovery between runs showed faster average training run times throughout the session and lower incompletion rates, despite no differences in perceptions of fatigue. In addition to the improved performance (run time), the importance of completion rates for technical and tactical skiing ability, and the greater risk of injury that accompanies incompletions, this is a critical implication of active recovery performed between runs for alpine skiers.
The logistical challenges of training environments restrict the type of recovery an alpine ski racer may be able to perform during a training session. This study showed that 3 minutes of moderate-paced walking with poles was effective at enhancing blood lactate clearance and improving performance compared with static recovery. Future studies should investigate the optimal timing of active recovery (i.e., bottom of the run vs. top of the run) and protocols of active recovery (i.e., walking vs. dynamic stretching) for lactate recovery. Additionally, the implications of blood lactate changes on objective performance (run speed) should be confirmed for all disciplines. Although classical studies exist examining the physiological demands of alpine skiing, many were conducted in the 1970s, 1980s, and 1990s. Although scientifically sound, these occurred before the equipment shift to carving skis and breakaway poles, which have profound effects on technique, energy demand, speed, and forces built/endured. Thus, further studies are needed to update our understanding of the demands of alpine skiing as it is experienced today.
The authors would like to thank Research Programs in Applied Sport Sciences for funding this projects; Jeff Lackie, Cam Twible, and Tommy Eckfeldt for their assistance and accommodation throughout the project; and all the current and former Men's and Women's Ontario Alpine team athletes for their participation in this study.
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