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"Sports-specific training – a break-down of the transfer effect"

A review of Siff & Verkhoshansky’s model of Dynamic Correspondence and the application of its principles between the power clean and the take-off phase in ski jumping.

When selecting exercises within a sports-specific training program, it might seem appropriate to incorporate movements replicating the skill in question, creating a better training transfer effect. For example, in Siff & Verkhoshansky’s seminal work “Supertraining”, the authors outline five criteria within their framework “dynamic correspondence”, which breaks down aspects of movement, force-production, effort, rate and time of maximal force production and the regime of muscular work. (1). This article will take the example of ski jumping (specifically within the take-off phase) and compare the dynamic correspondence of the power-clean weightlifting movement and whether the similarities of triple extension are enough to carry over into a positive training effect.

Criteria 1. How efficient is the movement?

The first of the five criteria, “amplitude and direction of movement”, could be described as the kinematic aspect, i.e., how we go about moving to express force and whether the exercise and skill look similar through the joints and angles within the movement. It emphasises the start position, joint range of motion, and muscles recruited (1).

The power clean starts at the beginning of the first pull with the spine and pelvis neutral, feet hip-width apart and angular displacement occurring at the hip, knee and ankle joints. The second pull requires explosive movement from the hips and knees and plantar flexing of the ankles into a fully extended position. Pulling action in weightlifting exercises from a biomechanical standpoint (2)

Within ski jumping, there are multiple complex parts to consider from in-run, take-off, flight phase and landing (3). When looking at the take-off phase in particular, as with the power clean, the hips, knees and ankles are held in a tucked or flexed position during the in-run phase. The phase requires explosive hip and knee extension to generate enough force before take-off. Equal pressure under the forefoot and heel helps the skier raise the centre of mass to achieve forward angular momentum into the flight phase. This aspect is critical for the skier to achieve optimum aerodynamics during flight (3).

Muscles recruited in the take-off phase of ski jumping are vastus lateralis, vastus medialis, gastrocnemius, tibialis anterior and gluteus maximus (4).

The power clean has been shown to recruit similar muscle groups to ski jumping with activation recorded via EMG, adding biceps femoris and erector spinae (5).

It is also evident that under loads more significant than 70% of 1rm other primary muscles such as transverse abdominis multifidus and trapezius, are also recruited.

In contrast to the power, clean EMG data collected on ski jumping gives reduced activation of the gastrocnemius and limited plantar flexion due to the stiffness of the ski boot; this inhibits the joint range of motion through the ankle into the extension (6). Interestingly, specific research papers have focused on this topic, discussing whether an athlete should perform exercises with limited ankle flexion and focus on the knee and hip extension to see what differences are created not just in joint range of motion but in force production and speed of muscle contraction (6).

Creating a similar training environment may achieve a more sports-specific exercise related to the skill. However, other variables that may not be accounted for during training might create a narrower association between the exercise and the take of the ski jumping phase, such as body mass, take-off angle, equipment, weather and course conditions (7).

The power clean and derivatives have kinematic similarities (except ankle range of motion) that could deem it a suitable (although not optimal) exercise concerning the first criteria from the principle of dynamic correspondence.

Criteria 2. Where is the most force, and at what angle?

The region of accentuated force production is the second criterion and focuses on where force production is highest and at what angle of the joint. It is stated that force production may increase most at different points between the skill and the exercise (1).

Through the various angles measured, many studies show that peak power production is at its highest during the power clean's mid-thigh or second pull phase (9). Peak power has been recorded with knee angles of 125° and hip angles of 145° (10). The previous authors stress strength and training maturity as essential factors in achieving and optimising peak force during the lift. However, within ski jumping take-off, many more variables than training maturity are worth mentioning to highlight the incredible complexity of the skill. Those factors that can interfere with the athlete achieving an optimum jump include body weight, altitude, weather conditions, set-up, and in-run (11), (12). When the latter are considered under optimum conditions, peak force seems to be highest at the point just before take-off (13). The previous literature discusses the most successful jumps over 106 meters being held by athletes with knee angles of around 140° and hip angles of around 110°, which, based on preliminary evidence regarding the exercise, seems to be in contrast (more specifically at the knee joint) to angles where peak force is optimum during the power clean. They concluded that the optimum set-up conditions for achieving peak power should be based on an individual professional athlete’s anthropometrics and capacity. Additionally, rapid knee and hip extension are critical in generating maximal jump forces and keeping the shank angle relative to the take-off table in the early stages to support the thigh into rotation. When discounting the take-off platform and putting athletes side by side, similarities in position can be seen in the first and second pull angles within the power clean and the tuck and take-off position of the ski jump.

Differences in upper body joint angles can be observed because the skier needs to achieve a more aerodynamic position and forward angular momentum to be ready for stable flight, resist coefficient drag and prepare for the landing (3). Setting aside all other variables that could add a further argument, such as individual set-up positions, anthropometric conditions, and the capacity of the jumper and focusing only on peak forces at the same joint range of motion between the skill and the exercise, it would seem that the exercise does not match the skill within the second criteria due to peak forces being achieved at different points during the movement. As with the first criterion, another jump exercise or derivative that more closely relates to the skill may be a better way to eliminate aspects that reduce performance concerning force production at optimum angles (14), (6).

Criteria 3. How much effort?

The dynamics of the effort in the power clean suggest that the overload principle is critical to increased force production and peak power (15). The maximum peak force output of the power clean has been recorded at 80% of 1rm (16). However, other literature suggests that loads between 60 and 80% have no significant differences in force output, and 70% 1rm is a middle ground for optimal loading (17).

The evidence would then point toward an athlete needing to increase capacity via training to achieve this (1). Siff & Verkhoshansky discuss that the effort exerted in training should be the same or not less than within the sports skill.

Peak forces at 70% of 1rm in the power clean (around 1,921.2 ± 345.16N) surpass average peak forces achieved within the take-off phase of ski jumping recorded in training simulations at about 752 ± 148N. It should be noted that training simulations do not consider the drag and lift forces acting on an athlete during the in-run, which have been estimated between 100-200N (6). According to Siff & Verkhoshansky, If a training transfer effect occurs, the correct force must be applied at the right time (1).

This would highlight that using a derivative from an adjusted position that emulates the desired outcome might seem closer to matching as it may help develop force at a more appropriate range of motion. In ski jumping, an athlete has little time to pull everything together to produce enough force and optimise flight time. Limiting the exercise movement within training to produce force at the optimum joint angle might be one way of creating a closer transfer effect of force, additionally improving set-up during the in-run phase of the jump as this seems to be crucial in getting the correct amount of force needed in order not to throw off the flight phase.

Criteria 4. How much effort and over how long?

The fourth criterion, rate and time of maximal force production, extends further from the third criterion, where it can be seen that time to maximal force production are often more significant than the time available (1). Again, this could be a problem within ski jumping, especially with the set-up for take-off arguably being the most critical factor in achieving a stable flight (18).It is evident with the power clean that the time to produce peak force at 70% of 1rm from first to second pull is close to 1 second (19). However, within the take-off phase, the time to reach peak force is around 300 ms, although some simulated jumps in practice have taken as long as 500ms (3). Considering this, it seems clear that reducing the work time and decreasing the distance for the bar to travel could be a more suitable method to produce peak power in a shorter time frame. In addition, derivatives of the clean such as a pull movement followed separately by a hang or high hang movement, may create a closer dynamic correspondence than the power clean itself to cut the time to reach peak force.

Criteria 5. What are the muscles doing?

The fifth criterion can be described as how the muscle is working. For example, with weightlifting movements such as the power clean, the muscle must work through the stretch-shortening cycle, isometric, concentric and eccentric contractions to complete the lift (20). In addition, when incorporating these aspects in preparation for take-off, the athlete must achieve as good a tuck position as possible to extend fully for optimal take-off (4).

This shows similarities with the clean in terms of holding, shortening, and lengthening the preparation for take-off. Although the muscle works similarly throughout the exercise and the skill, as previously stated in the first criterion, different muscle groups are active at other times depending on the angle. That said, the similarities in how the muscle works are close enough between the skill and the exercise. Incorporating the evidence achieved so far, it seems clear that it is possible to match the skill with an alternative exercise to gain a better transfer effect.

So, does the power clean transfer to ski jumping, then?

Although the power clean and the take-off phase of ski jumping may look similar in terms of kinematic and kinetic similarities throughout the lower body from the start position to the point of peak force production or into the second pull, the affect similarities of the movement leading on to the peak force similarities are significantly different. Additionally, the effort required to achieve maximal force throughout the power clean is exaggerated compared to the controlled effort needed to set up an optimum flight pattern during take-off. Moreover, the time to produce peak force in a power clean at 70% 1rm is around 1 second (19). Within ski jumping, the variables contribute to an athlete’s ability to achieve optimum force on top of the actual time they may have. This could create difficulties when trying to generate a training transfer effect. It can also be seen that the way the muscle works will be affected by the kinematics within ski jumping; for example, a lack of plantar flexion forces other muscles to contract (6).

Overall, it seems crucial that an athlete uses exercise in general preparation for skill and as “force is king”, weightlifting movements seem to be a critical aspect of achieving a better performance in timing, strength, and explosive power (1).

Based on the method of dynamic correspondence, sports-specific training is one way of breaking down an athlete’s movement to increase performance. Still, it could also bring the analogy of a “sledgehammer to crack a nut”. Moreover, the lack of environmental similarities in sports-specific training may play a significant role in a transfer effect during competition.

However, suppose optimal force production and time to get there are critical.

In that case, derivative and ballistic exercises might be better suited for more neurological development to improve the athlete’s intent and save time, energy, and potential injury risk.

Reviewing the main points within this article and comparative literature, it could be feasible that there may be a bias whereby the athlete may focus too much on a specific area within a lift to increase their ability in a real-world scenario. Moreover, we can see that a clear understanding of a transfer effect is necessary for sports performance to ensure the athletes and coaches spend time and effort in the proper training area for any sport. In this case, the power clean does not match the proposed five criteria; therefore, an adapted approach must be applied. This gives credit to Siff & Verkhoshansky’s method in light of criticism of the transfer effect. The 5 criterion enables us to break down the skill to understand what might give rise to better coaching practice and transfer to performance in sport.


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