INTRODUCTION TO THE SPORT OF ALPINE SKIING
Alpine ski racing has been an Olympic sport since 1936, and currently, it consists of 6 events: Slalom (SL), Giant Slalom (GS), Super-Giant Slalom (SG), Downhill (DH), Combined (C, 2 runs of SL and 1 run of DH), and Super Combined (SC, 1 run of SL and 1 run of SG or DH).
GS and SL are referred to as the technical events, and these consist of 2 timed runs, with a 45-minute course inspection before each run, and the athlete with the fastest combined time wins. SL consists of gates 4–13 m apart; however, recent rule changes may restrict SL to as short as 9 m in some age-groups. Course times are typically 60–90 seconds (2,48), and courses are required to have a vertical drop of 140–220 m (below 100 m for SL and below 200 m for GS in children’s racing) (48).
The other technical event, GS, consists of gates approximately 18–25 m apart, with speeds ranging 40–80 kph (20–50 mph). Course times are also 60–90 seconds in duration, with a vertical drop of 250–450 m (48). For this reason, few courses have vertical drops of this length without at least 1 substantial flat section.
The speed events consist of SG and DH, and the winner is the fastest fastest run, where athletes remain in a tuck position for most of the course. remain in a tuck position for most of the course. The SG events occur on a single day with a 45-minute inspection of the racecourse (48). Gates are 25–40 m apart with a course vertical drop of 350–650 m (250–400 m for children’s racing) (48). Speeds can reach as high as 113 kph (70 mph) but are typically between 88 and 105 kph (55–65 mph).
Downhill requires at least 1 and up to 3 training runs on days leading up to the competition, with about an hour course inspection allowed each day. In DH, there can be “speed controlling” turns placed in the course at the officials’ discretion to maintain reasonably safe speeds; however, there are usually as few turns as possible (48). Speeds have been recorded up to 160 kph (100 mph) (12), but they are typically between 95 and 120 kph (60–75 mph), with run times from 1 minute to as long as 2.5 minutes, and vertical drops ranging from 450 to 1100 m (48).
Because the role of a strength and conditioning professional has gone from preparing for a specific sport task and competition to training for the physical demands of sport practice, it is important to understand the schedule and physiologic demands of a typical sport training session.
ON-SNOW TRAINING SCHEDULE
The schedule of a training day includes 1–4 warm-up runs, 1 inspection run of a training course, with 3–8 training runs on the course and 0–4 additional runs to help maintain the snow conditions on the course. Thus, training sessions last 2–4 hours with a total of 4–14 runs. A ski run can last from 1 minute to 10 minutes in duration with a rest break of riding a chair lift lasting for 5–15 minutes (41). Some training centers are accessed by high-speed detachable quads, which can double the volume of vertical distance during a training session. Also, some alpine training centers have installed ground lifts (T-bars and pama lifts), which increase the number of runs per session as well. Although the runs tend to be less vertical drop than chair lift access training centers, these typically will involve a high percentage of aggressive skiing per meter of vertical drop. It is also not unusual for athletes to do 2-a-day sessions, especially for youth athletes on weekends or during training camps.
PHYSICAL DEMANDS OF ALPINE SKIING
THE CARVED TURN
The most important aspect to all alpine ski racing events is maintaining a carved turn and resisting the forces generated (G force) during a turn while maintaining edge control and balance. Centripetal force (F) is equal to the mass (m) of the object multiplied by velocity (v) squared all divided by the radius (r) of the turn (Equation 1). In addition, the steeper the slope of the hill, the more the force vector of gravity (g) is added to the centripetal force of the turn, which is especially apparent from the apex of the turn through completion (Equation 2).
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Therefore, as either the radius of the turn becomes shorter (quicker turn) or the velocity increases, the forces that must be resisted to maintain balance and technique can increase dramatically. Thus, the ability for the lower body to maintain adequate forces to resist snow reaction forces and maintain the dexterity needed for edge control is critical for alpine skiing success.
The turn is typically broken down into 4 phases: the initiation phase, turning phase, completion phase, and the transition phase (see Figure 1). In the initiation phase, the uphill and outside leg supports the body weight and the skis roll on edge as the shoulders move toward the gate. In the turning phase, the shoulders become level with the snow surface, outside leg remains long, and the inside leg bends as needed to allow the hips to move close to the snow, creating a high edge angle. In the completion phase, the hips rise up and the outside leg starts to bend, decreasing the edge angle of the skis. In the transition phase, the feet move under the hips, as the hips move down the hill, and the body weight transfers from the downhill ski to the new uphill ski. At all times, the athlete should have “cuff pressure,” meaning that the shin is in contact with and applying pressure to the front of the boot. The upper body should remain balanced and stable, without excess arm movement.
Figure 1: Phases of a typical carved turn in an alpine ski racing course.
BIOMECHANICS
Biomechanical analysis of alpine skiing has identified key muscles and movement patterns needed to maintain balance and edge control through the carved turn. A pivotal study by Hintermeister et al. (17), who monitored electromyographic (EMG) activity of lower leg, thigh, and trunk muscles during both SL and GS of U.S. and British National Team members, concluded that the primary role of quadriceps muscle groups was to maintain balance while the ski carves through the turn, and projecting the hips forward during the completion as the skis come under the body to release energy from being bent in the apex of the turn. Additionally, the activation of the tibialis anterior was shown to be critical because dorsiflexion pulls the body at a forward angle toward the tip of the skis, maintaining symmetrical fore-and-aft balance as the skis move forward and laterally under the skiers body (22,45). Sustaining this symmetrical fore-and-aft balance over the skis has been shown to correlate with SL ski performance (22,45). Not surprisingly, this group also showed that EMG activity of muscles around the knee and hip was highest in the turning phase, where centripetal forces are greatest. In addition, the rectus abdominis muscle had the greatest EMG activation from the middle of the turning phase (apex) through the completions of the turn, where ski-snow reaction forces are greatest, which parallel the novel core pulse theory described by McGill et al. (30,31).
The hamstrings and gluteus also play essential roles in the eccentric absorption of terrain because these are active during the transition and turning phases (17). The hamstrings have a short rest, typically during the first part of the completions phase, as the knee extends without simultaneous hip extension, but as the hips extend, the transition phase starts, and they become more activated (17). The gluteus have a slightly different activation pattern for SL where they are not active in the completions phase but in GS are very active at the end of the turning phase and beginning of the completion and are inactive through the first half of the transition phase of the next turn (17).
FORCES AND JOINT ANGLE VELOCITY OF ALPINE SKI RACING
The forces generated in alpine ski racing turns are generally between 1 and 2.5g with peak forces within a course or landing from a jump to exceed this range in world cup–level athletes. In 2 studies using several camera angles, calculated peak forces in SL turns were 2–3g (44,46). Using a Pedar Mobile system on a FIS, SL course with a 17° slope forces were measured to be 1.5g with the force predominately going through the forefoot, suggesting that this takes advantage of the steering nature of the front of the ski (26).
Investigations comparing maximal strength at various angular velocities have found alpine skiers to have particular increases in strength relative to other athletes at slow velocities on AV Hill’s force-velocity curve theory (24,49). This theory describes how the maximal force increases as the concentric velocity of a muscle decreases, becomes isometric, and increases in eccentric velocity (24).
One turn typically requires 1 set of knee flexion (eccentric) through the first half of a turn and knee extension (concentric) from just after the apex of the turn through completion. What is important to the strength and conditioning coach is the angular knee velocity for each event: SL, 69 ± 11; GS, 34 ± 2; SG, approximately 17°/s. These are much less than recorded in a typical running gate (300°/s) or during sprinting efforts (600–700°/s) (49). This is combined with relatively long movement cycling times (time to complete a left and right turn; SL, 1.6 ± 0.2; GS, 3.5 ± 0.6; SG, approximately 4.1 seconds) (49) and relatively high percentages of maximum voluntary contractions (SL, 74 ± 33%; GS 73 ± 21%), with maximum strength requirements exceeding 100% of laboratory recorded maximal voluntary contraction (42). This creates a situation where muscle blood perfusion is reduced, with relatively slow muscle movements as compared with other anaerobic dominated sports. Knee extensions as low as 20–45% of maximal voluntary contraction of the quadriceps muscle group can restrict blood perfusion (9). Turnbull et al. (49) suggested that there is a unique cardiovascular adaptation to allow for greater blood flow during the transition period between turns; this combined with the vibration exposure (see below) makes the time for on-snow skiing an important stimulus for developing metabolic energy supply adaptations specific to alpine ski racing.
VIBRATION IN ALPINE SKI RACING
In addition to the high force demands, alpine skiing has additional hypoxic stress that can compound, which include the relative altitude, the length and force of the muscle contractions, and the vibration stress caused by the ski snow contact. Recent investigations have quantified the effects of vibration on ski performance from a metabolic and mechanical perspective. Vibrations in alpine skiing depend on the snow conditions, equipment (skis and boots), velocity, point in a turn, turn shape, and event (11). Vibration forces during free skiing have been measured on the ski boots to be as high as 30g with frequencies of 5–30 Hz, in experienced skiers (11). EMG of major lower-body muscle shows significant positive correlations with vibration acceleration data (28). The ability to dampen vibration forces has been shown to be inversely related to the frequencies of the vibrations, with 30% occurring at the hip and 20% at the neck for 10 Hz but less than 12% occurring at the hip for vibrations higher than 60 Hz (11). Thus, as the vibration frequency increases, the body has a reduced ability to dampen it. Dampening occurs from an improved muscle tendon tension (muscle tone) for a flexed ankle, knee, hip and spinal column seen in alpine skiing technique and passively from soft tissue and cartilage (11). The dampening of these forces are not only needed to maintain smooth gliding of the skis to conserve speed and tactical positioning on courses but also needed to maintain visual field search (40) and reduce additional perturbations to muscle blood supply.
It has been hypothesized that during vibration stress, in microblood vessels, red blood cells are jostled laterally in the capillaries, causing damage to vessel walls and decreased velocity of blood flow (32). This increases total peripheral resistance, which has been measured between 10 and 20% (32). Mester et al. (33) showed that phosphocreatine (PCr) depletion of 20% occurred from a 100-second contraction of the gastrocnemius muscle increased to 50% and 95% when a vibration load of 8 Hz was added for contraction lengths of 60 and 80 seconds, respectively. Alone vibration and occlusion have not shown to decrease intramuscular pH, but the combination has shown decreases (32). Thus, the duration of the increased muscle tension needed to dampen vibration and the long eccentric and concentric muscle action in a carved ski turn reduces blood supply to active muscle tissue. A desirable training adaptation from extensive endurance training increases capillary density, which would be the best mechanism for increasing muscle blood supply during high levels of vibration stress. Thus, for alpine skiing, vibration stress should be viewed not only from the traditional strength perspective but also from a bioenergetics perspective.
Investigations into the efficacy of vibration training in the strength and conditioning room induce adaptations in neuromuscular firing that increase the dampening capabilities of the muscular skeletal system have shown some promise. In a pilot study, Spitzenpfeil et al. (43) compared elite-level hurdlers, hockey players, and alpine ski racers and showed that as the vibration demands of the sport increased, so did the dampening abilities the athletes. Additionally, these groups showed that with 8 sessions of vibrations training, with 4 sets of 12 repetitions of squats with 60% 1 repetition load on a vibration plate set at 24 Hz at ± 2.5 mm of amplitude the dampening ability of all the athletes was increased (43). However, it has yet to be shown if improvements in vibration dampening ability from the supplemental vibration training carry over to sports-specific vibration dampening and improves sport performance. Therefore, it is currently recommended that the adaptations of vibration be left to those induced by training for the sport. With one caveat, the athletes with limited on-snow training time might have a benefit from supplemental vibration plate training.
ENERGY SUPPLY FOR ALPINE SKIING
Alpine ski racing is a high intensity short duration sport that relies primarily on the phosphogenic and glycolytic energy systems. When differentiating the total yield of energy supply to complete a GS run, no recent data is available. Turnbull et al. (49) discussed 2 studies from ‘84 and ’85, which makes interpretation difficult as physiologic measurement accuracy is unknown; however, more recent evidence has shown no differences in metabolic utilization between traditional and carved turn skiing (8,38). Saibene et al. (39) reported that 28.3% came from the ATP-PCr energy system, 25.3% was buffered through the lactate energy system, and 46.4% (net O2 uptake) came from the oxidative system. Veicsteinas et al. (50) reported that ATP-PCr system contributed 25–30%, lactate approximately 40%, and the aerobic system contributed just 25–30%. Although aerobic energy capacity accounts for nearly half of the total energy used, it is in support or buffing of the ATP-PCr system and lactate shuttling. A study looking at myoglobin and hemoglobin desaturation differences has shown that GS has higher depletion rates than SL, which was contributed to the vascular profusion deficits as a result of prolonged muscle contractions in GS, maximal voluntary contraction levels of >50%, and vibration loads (47). The increased anaerobic demands of the sport are supported by blood lactate accumulations of 12–15 mmol/L in Austrian National Team athletes after a competitive world cup run (event and course length were not reported) (1,10,35,41).
The optimal range for aerobic fitness in alpine ski racers has been a matter of debate (35,36). Von Duvillard et al. (52) observed that during a GS course of 40 gates which took approximately 60 seconds to complete in 9 (16.1 ± 1.4 years) high school skiers attending an eastern US ski academy during training used only approximately 50% V[Combining Dot Above]O2max while skiing the course. But others have reported energy demands for the technical events (SL and GS) to be 160–200% of V[Combining Dot Above]O2max, and approximately 80–90% V[Combining Dot Above]O2max for speed events (DH) (12). The heart rates during GS training of elite skiers reach approximately 87% heart rate max (HRmax) as compared with collegiate skiers (SL and GS only in NCAA) who reach 97% HRmax and older recreation skiers who free ski (no course) reach approximately 80% HRmax (41). Elite skiers were also able to reach higher HRmax than their recreational counter parts (95% versus 65–75% HRmax, respectively) (1). However, the V[Combining Dot Above]O2max of elite alpine skiers is the equivalent of recreationally trained field sport athletes (∼55 mL.kg−1.min−1) (see Table 1). In a study of the Austrian National ski team over 3 years and 3 groups, only the speed group had a significant correlation between aerobic power and sport ranking, for 1 of the 3 years (35).
Table 1-a: Review of key human performance values that have been reported in elite alpine ski racers
Table 1-b: Review of key human performance values that have been reported in elite alpine ski racers
Table 1-c: Review of key human performance values that have been reported in elite alpine ski racers
Combining these energy demands, decreased muscle blood perfusion (see above), and course lengths of 60–150 seconds leads to a great deal of oxygen deficit and subsequent acid buildup, as indicated by blood lactate levels described above in elite-level alpine skiers. Therefore, it seems logical from data available that alpine skiers should work toward developing a lactate threshold and lactate tolerance through interval training at or above their lactate threshold, as this will obtain the relatively low V[Combining Dot Above]O2max seen in the elite athletes of the sport, while maximizing the anaerobic fitness, which is the primary cause of fatigue in the sport.
ANTHROPOMETRIC DATA
Anthropometric data of elite-level alpine skiers as reported can be seen in Table 2. Age and competition level are as reported by the studies, and data organized by male and female from highest level of competition to lowest level, and then by age from oldest to youngest. Values are mean ± standard deviation.
Table 2-a: Anthropometric measurements of competitive alpine skiers in descending ages and level
Table 2-b: Anthropometric measurements of competitive alpine skiers in descending ages and level
COMMON INJURIES AND MECHANISMS
ANTERIOR CRUCIATE LIGAMENT INJURY
Anterior cruciate ligament (ACL) injuries make up 10–20% of all skiing injuries and have a unique mechanism in elite alpine ski racers when compared with recreational skiers (4). ACL injuries occur during both knee extension or full dynamic flexion with the addition of one or a combination of anterior draw of the tibia, internal rotation, or external rotation (16). A small portion of knee injuries come from crashing and tumbling into nets or other obstructions (4). Noncontact or noncrashing mechanisms include slipcatch, dynamic snowplow, and back-weighted landing (4). Slip-catch is the most common and occurs during a turn where the outside ski leaves the ground and then with an extended leg initiates a carved turn across the body, causing an internal rotation as it comes back into contact with the snow (4). The dynamic snowplow consists of a deep knee and hip flexed position, where the ski catches an edge and turns quickly under the skier, causing rapid internal rotation (4). The back-weighted landing is characterized from a landing where the tail of the ski hits the ground and causes anterior draw of the tibia and tibiofemoral compression with additional internal or external rotation if the body is twisted (4). Fortunately, the invention of the spring-loaded release binding has reduced the total injuries (all lower-body injuries) from 5–8 to 2–3 per 1000 skier days, by providing a valgus release mechanism (34). However, only a few companies have a toe lift release mechanism, to limit the maximum anterior displacement force of the tibia relative to the femur.
For the strength coach, interpreting this injury mechanism, which is season ending and can be career ending, has become the underlying rationale for the dynamic hip mobility training and integration of strength in balance training described below. The purpose of this type of training is to increase the neurologic motor patterning, dynamic knee stabilization reflex, and functional range of motion for the knee and hip in the extended and flexed positions. Athletes develop the proper co-contraction of the hamstrings and quadriceps, in a deep squat position, as well as an upper-body balance to reduce the ability for the upper body to fall backward, which, if occurs, will diminish the co-contraction forces that the hamstrings can provide to counter the anterior displacement forces on the tibialis. Evidence supporting this hypothesis is that athletes who went 3 years without an ACL injury had a peak hamstring torque at a significantly deeper flexion angle (25.4 versus 22.2, SD not reported) than those that did sustain an ACL rupture when monitoring 41 US freestyle international level athletes (20). This investigation also observed no predictive value for measures of hamstring to quadriceps ratio (20). The implementation of hip mobility training that increases the functional athletic ability of alpine ski racers in the deep squat position has been used and may be effective in reducing ACL ruptures.
SHOULDER INJURIES
In alpine skiing, shoulder injuries make up 4–11% of all injuries and 22–41% of upper extremity injuries, with the 4 most prominent being 1) rotator cuff contusion, 2) anterior glenohumeral dislocation/subluxation, 3) acromioclavicular separation, and 4) clavicle fractures (23). Falls provide the mechanism for most injuries, which include a direct “blow to the shoulder, an axial load from an out-stretched arm, or an eccentric muscle contraction associated with resisted abduction by the slope during a fall” (23). A secondary common mechanism for injury in alpine ski racers in GS, SG, and DH occurs when a skier hooks his or her arm between the 2 gaits and below the panel connecting them, which can cause the arm to be pulled violently into horizontal abduction and internal rotation. However, because the gate has a spring-loaded hinge at the snow level and the panels are designed to slip off the gate, an athlete with sufficient isometric strength and shoulder stabilization can pull the panel off and continue down the course without injury or penalty. In cases of shoulder injuries in alpine ski racers, the strength coach should work closely with the sports medicine staff to ensure the implementation of a shoulder rehabilitation program and respect the need for both upper-body maximal strength and strength endurance to reduce the injury risk.
PROFILE OF PERFORMANCE TESTS
A selected set of performance measures of elite alpine ski racers can be found in Table 1. Data were chosen from studies that reported international, semiprofessional, and top ranking junior level athletes. Because only a few studies reported the specialty of athletes, technical, speed, or all around skiers, data could not be separated out by specialty. The data are reported with the same order as in Table 2. Testing equipment and methods and details important to testing protocols are also listed. Countermovement jump, average of 5 countermovement jumps, 1 repetition squat, V[Combining Dot Above]O2max, and cycling ergometer wattage at 4 mmol of lactate (lactate threshold) are all tests and methodology standard to human performance laboratory or field testing.
Unique to alpine ski racing are the hex test and the 90-second lateral box jump test. Because these protocols are uncommon in the literature, below is a brief but usable description.
The hex test consists of 6 hurdles 61 cm wide with the following heights in clockwise order: 20, 35, 20, 25, 20, and 32 cm (Figure 2A). Facing the same direction throughout the test, the athlete does 3 revolutions of the hexagonal obstacles with 2-footed jumps as quickly as possible, with the start and finish positions in the center of the circle (Figure 2B). The time to complete without touching a hurdle is recorded (37).
Figure 2: Hurdle dimensions and movement pattern for the hex test.
The 90-second lateral box test consists of a box that is 40 cm high, 60 cm long, and 51 cm wide (Figure 3). The athlete starts on top of the box, jumps down to the right side, then back to the top of the box, briefly touching it, and jumps down to the lefts side in a lateral fashion and jumps back up on top of the box, briefly touching it and then back to the right side, and so on. Each time the athlete touches the top of the box, it counts as 1 jump; the score is how many jumps the athlete can do in 90 seconds. With junior athletes (<16 years old), some coaches have used a 60 second test. (37).
Figure 3: Box dimensions and movement pattern for the 90 second box jump test.
STRENGTH AND CONDITIONING PROGRAM
The purpose of a strength and conditioning program for alpine skiers is to maximize lower-body strength, explosive power, a focus on low-velocity (primarily eccentric) force production, and developing the anaerobic metabolism, specifically developing the lactate threshold and lactate tolerance. The macrocycle for alpine ski racing can be broken down into 5 mesocycles: 1) active recovery, 2) off-season hypertrophy, 3) preseason strength, 4) preseason strength endurance, and 5) in-season maintenance and peaking. Although the exact periodization and program for an athlete is individual; example 2-week programs for each mesocycle can be seen in Table 3, with workouts described in Tables 4 through 9. The active recovery is similar to other sports and should allow the athlete to enjoy physical activity, while providing enough metabolic work to maintain the oxidative metabolism. This typically occurs in mid April through May. In June, the off-season phase should start and focus on hypertrophy and developing a technical base for Olympic and power lifting exercises that can be used in the next mesocycle. The preseason phase should span September and October and focus on developing strength and power, while preparing the athlete for early season on-snow training in November. The in-season phase should start in late November and early December, focusing on maintaining strength and power while developing the anaerobic buffering system for peaking in mid January through February. For elite athletes prequalified for championships, peaking should occur later in the season, as the championship races tend to be in early March. The next section will provide a brief justification for each type of training presented in the example mesocycles and provide examples for each one.
Table 3-a: Prototypical weekly programs of mesocycles commonly employed for alpine ski racing
Table 3-b: Prototypical weekly programs of mesocycles commonly employed for alpine ski racing
Table 4: Prototypical Strength Workouts
Table 5: Prototypical mobility workout and descriptions
Table 6: Prototypical plyometric workouts
Table 7: Prototypical eccentric focused workouts
Table 8: Example recovery workout
Table 9: Example anaerobic energy system workout
STRENGTH AND POWER
Axial loading exercises, such as the squat, deadlift, cleans, and snatches, should be the foundation for developing full-body structural support in high G-force alpine skiing turns. However, the use of leg exercises that do not provide axial loading are beneficial for 3 reasons: 1) extensive axial loading is not seen in alpine skiing because the center of mass of the body is around the navel region when the G-force increases, 2) the increased prevalence of kyphosis in the upper back region from the rounding of the upper back in a ski stance, and 3) heavy axial loading without proper progressions can exacerbate back injuries. Exercises such as sled leg press or belt squats can be used for athletes with lower back pain who do not tolerate heavy squat or deadlift exercises. Thus, supplementing closed and open chain exercises for the lower body will help increase lower-body maximal strength, while not limiting training to the fatigue level of the spinal column–loaded exercises. Example strength and power workouts can be seen in Table 4.
UNILATERAL STRENGTH TRAINING
In addition, unilateral lower-body and upper-body training has efficacy. During alpine skiing turns, especially in GS, SG, and DH, the inside ski (closest to the turning gate) can be off the ground with knee and hip in deep flexion. Thus, exercises such as single-leg squat, leg press, lunges, and step-ups are beneficial to promote unilateral balance and mobility during high-force situations (3).
STRENGTH AND BALANCE TRAINING
Alpine skiing is characterized by the instability with ski snow contact, especially in soft snow and rutty course conditions. The purpose of strength and balance workouts is to improve motor patterning for unstable conditions through neurologic adaptations. Adding an instability component to strength training or plyometric training workouts, with the use of equipment such as balance discs and stability balls has been shown to improve neuromuscular motor patterning. This leads to improved coordination and confidence in performing a skill and a decrease in co-contraction during the instability (3). However, because of the increase in co-contraction for this type of exercise, the force output during strength and balance exercises is diminished (3). Thus, it should be used as a supplement to more stable strength workouts that have higher force production and subsequent improvements in maximal strength and power at given velocities (3). These types of workouts are ideal for days in which high force production (power and heavy strength workouts) do not make sense when implementing a functional nonlinear periodization (25). Table 4 shows an example workout.
DYNAMIC MOBILITY TRAINING
A recent trend in strength and conditioning for alpine skiing has been the implementation of dynamic mobility exercises. Although little has yet to be written about this type of training, the basic principles are found in theories of exercise science. The purpose of mobility training is to increase the functional range of motion for synergistic muscles, specifically biarticular muscles and muscle groups of the hip girdle that have small ranges of motion during normal gate and running sports usually less than 20% of physiologic range of motion (27). For instance, the hamstrings during normal gate and hopping actually have an eccentric and concentric action during the acceleration phase based on the joint angle velocities of the hip and knee, as its function is to transmit force from the quads during knee extension to the hips for simultaneous hip extension (27). Also, as the quadriceps extend the knee, the gastrocnemius transmits force to put the ankle into plantar flexion. In addition, during normal gate, other muscles simply have a smaller used range of motion compared to what are common in the sport of alpine skiing. Such muscles include the gluteus maximus and medius, which work to help maintain postural alignment during the swing phase of walking gait (one foot in contact with the ground). Dynamic mobility exercises typically are designed to target 1 or 2 of these muscle groups at a time, with body weight or light external loads. As a result of the long moment arms for some of these exercises, the force loads on muscles can be as high as a 10 repetition maximum but are typically much less.
The purpose of dynamic mobility training for alpine ski racers, as mentioned above in the ACL injury section, is to increase the athletic ability in standing and deep squat position. More specifically, the purpose is to provide enough hamstring flexibility so as not to allow the upper body to fall backward in a deep squat position, or the legs to abduct or adduct, while also providing enough ankle flexion, so the center of mass can remain forward between the feet and toes. Because of the instability of the sport, it is not uncommon for these exercises to include a balance component, but it does not typically contain a power or maximal strength component because of the extreme range of motion. Because these exercises are not typically found in the exercise description literature, example exercises, photographs, and a description with progressions can be found in Table 5 and Supplemental Digital Contents 1 through 7 (see Videos, https://links.lww.com/SCJ/A98; https://links.lww.com/SCJ/A99; https://links.lww.com/SCJ/A100; https://links.lww.com/SCJ/A101; https://links.lww.com/SCJ/A102; https://links.lww.com/SCJ/A103; and https://links.lww.com/SCJ/A104).
SPEED EVENT SPECIFIC TRAINING
Because speed events require athletes to hold an aerodynamic or tucked position for the majority of the course, incorporating this body position when possible in exercises will help to increase the carry over effect of a strength and conditioning program. Because holding a tuck position will change the motor recruitment pattern, the motor units used during tucked turns and gliding will most likely be trained by the strength and conditioning program that includes exercises such as tuck jumps, walks, and stability drills. However, it is not recommended to use this rounded back position when adding external load above the hips.
SPORT-SPECIFIC CORE TRAINING
Ski coaching literature talks specifically about maintaining level shoulders through the turn and resisting the forces that pull-down on the inside shoulder (shoulder closest to the center of the turn or gait), thus elevating the outside shoulder. To maintain a strong stable upper body through the turn, a synergistic tension in the shoulder, hip girdles, and core muscles is needed. The quadratus lumborum provides lateral spine flexion in the lumbar region, which is critical to maintain level shoulders during a turn. Although it is not always necessary to increase strength in these muscles and related muscle groups, it is, however, important to increase strength endurance overall. Given that turns per course range from 30 to 70, building up to repetition volumes of 15–30 per side with light to heavy external loads in a core workout routine is warranted, especially in athletes with limited on-snow training time.
PLYOMETRIC/JUMP/CHANGE OF DIRECTION TRAINING
Enhancing vertical power and change of direction has been used to help with the quick reactions required to maintain tactical course positioning and to make adjustments to the terrain. Explosive power has been justified in several correlation studies where explosive power as measured by countermovement jump height and the average of 5 continuous counter movement jump heights in 26 (12 men and 14 women, age, 17.1 ± 0.9 years) elite alpine skiers at an eastern U.S. ski academy has shown predictive ability for alpine skiing sport performance (52). The correlation coefficients of the highest vertical jump height with USSA national point ranking system was −0.46, −0.60, −0.43, and −0.53 for SL, GS, SG, and DH, respectively (44). For the average of 5 vertical jumps, the correlation coefficients were −0.44, −0.63, and −0.58 for SL, GS, and DH, respectively; the correlation with SG was not significant (p ≥ 0.05), and all others were significant (52). Mean and standard deviation for these tests can be seen in Table 1. A similar field test reported in 1988 by Andersen et al. (1), which used 5 continuous double-leg long jumps, had a very strong correlation (r = 0.89) with GS skiing performance (measure of performance not reported). This study reported that the Canadian men’s national team members reached 14.1 m, regional skiers reached 13.1 m, and club skiers reached 10.8 m. These moderate-to-very strong correlations indicate that the physical ability to produce rapid force production and to maintain it over 5 jumps corresponds to sport performance and should be a focus of a strength and conditioning program. Although testing was performed in vertical and forward movements, many programs also include a change of direction, slope, unstable surface (sand), and reaction components to these workouts, to help prepare athletes for the quick reaction times needed for both visual search and proprioceptive responses while going down a course. Table 6 shows an example workout. However, it is not clear that the correlation between explosive power and sport performance is causation, as high strength during low-velocity eccentric and concentric movements that characterize the sport (see above) is determined by the same motor units (type II) that effect explosive power performance.
ECCENTRIC TRAINING
Because the carved turn is a prolonged eccentric component and the sport requires the absorption of terrain, which is primarily accomplished through eccentric muscle action, the idea of eccentric dexterity to describe this may have its origins with a preliminary finding from Hoppeler and Vogt (18), who showed that the ability to more finely modulate eccentric force had a very strong correlation (r = 0.93) with percent standard deviation for target eccentric cycling force during a 20-minute effort to whole-season SL FIS points, in a group of 15 elite junior alpine skiers (18). In other words, athletes who could more accurately adjust the level of eccentric force to a dynamic target wattage reading output on the eccentric ergometer computer were also subsequently ranked as better SL athletes using a FIS point list—an international skiing sport ranking system. Interestingly, it has been shown in GS skiing that approximately 1.0 ± 0.2 seconds is spent in eccentric muscle action of the quad, with only 0.5 ± 0.1 seconds spent in concentric muscle action (5). Providing evidence that a skier can finely adjust ground force reactions against the snow during eccentric movement is a highly important skill for ski racing success.
Although improving eccentric dexterity is primarily accomplished through on-snow ski practice, the supplementation of eccentric training could potentially assist in this ability. Eccentric overload training or eccentric cycle ergometer training would also assist in the effort to increase maximal strength and explosive power. Eccentric overloading is a method of training where there is additional load for the eccentric portion of a lift that is 110–120% of the eccentric-concentric 1 repetition maximum load. This has shown to be beneficial in causing hypertrophy of the type IIA and type IIX muscle fibers and subsequent improvements in vertical jump performance as compared with a training program using the same concentric/eccentric load, in a 6-week long training study, with 24 trained male athletes, using an 8 repetition maximum load, on a specialized knee extension device (13). However, this type of training can be performed using stable weight machines, which allow for one limb (both legs or both arms) to perform the concentric portion of the lift, then one limb can hover just off of the machine during the eccentric portion of the lift, thus doubling the eccentric load for the limb lowering the weight down. This can be performed on machines such as leg extension, leg press, chest press, and seated row. An example workout is shown in Table 7.
A second type of eccentric training involves the use of an eccentric ergometer. Hoppeler and Vogt (18) found beneficial performance gains in 15 alpine ski racing athletes starting at 400 watts for 20 minutes and progressing to loads as high as 800 watts within 5 training sessions on an eccentric cycle ergometer. Volumes in one study were 20 minutes, 3 days a week, with an additional 40 minutes of traditional strength training. This study showed an 8% (4.1 cm) increase in vertical jump height, where a control group had no change in height despite equal amount of traditional based strength training (18).
SUMMARY
The purpose of a strength and conditioning program for alpine skiers should be to maximize strength, throughout the force velocity curve with emphasis on eccentric force production and explosive concentric power production at slower velocities and to develop strength endurance—capacity to maintain force and dexterity of force from 45–150 seconds. As disqualifications and injuries typically occur from falling and crashing, the goal of a portion of the strength and conditioning program should be to develop quick reaction times for both visual field search and proprioceptive ability along with strength endurance and functional mobility to avoid a crash. In addition, because an athlete may ski as much as 4–7 days a week, season long durability is critical. Bacharach and von Duvillard (2) stated that it is possible to change the physical characteristics of athletes, without affecting their skills as a skier and improve their national rankings. Thus, a program that focuses on maximal lower-body strength development, explosive power, quickness, glycolytic buffering capacity, and improving the lactate threshold should reduce injury risk and improve sport performance.
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