Deceleration Insights for Team Sports With Damian Harper

 

Damian Harper is a senior lecturer and course leader of the MSc Strength & Conditioning program at York St John University in York, U.K. He is an accredited sport and exercise scientist (BASES) and strength and conditioning coach (UKSCA). Damian is currently studying for a Ph.D. at the University of Central Lancashire, examining “the determinants of proficient deceleration.” He is also currently the lead for physical performance conditioning at one of the Football Associations’ Tier 1 Regional Talent Clubs (RTCs) for development of elite girls’ soccer in the U.K.

Freelap USA: Could you share the value of the 10/5 repeat jump test (RJT) with coaches? It seems the idea of getting more jumps and filtering the data slightly is an excellent field test during training. Could you briefly share what it is and why it’s worth doing for those that only know the classic RSI test?

Damian Harper: The 10/5 RJT was a protocol I designed as part of my MSc thesis back in 2011, to specifically evaluate an athlete’s repeated rebound capabilities (i.e., reactive strength). It was part of a more comprehensive testing profile we used for a group of English Super League Rugby League players. The key aim was to develop a protocol that would be sensitive to detecting training-induced changes in reactive strength performance, be quick and easy to administer in the field, and require limited practice from an athlete’s perspective.

The 10/5 RJT simply requires athletes to perform a series of 10 repeated rebound jumps with a ground contact time (GCT) of less than 0.25 seconds. Instructions given to athletes are simply to “minimize GCT” and “maximize jump height.” All that is required by coaches is some measurement device to obtain GCT and flight time (FT). I have preferred to use the SMARTJUMP contact mat, which can provide real-time visual or audio feedback on each individual GCT within the rebound series—thus allowing athletes to make any necessary technical adjustments.

Video 1: The 10/5 repeat jump test requires athletes to perform a series of 10 repeated rebound jumps with a ground contact time (GCT) of less than 0.25 seconds. Coaches only need a measurement device, like the SMARTJUMP contact mat, to obtain GCT and flight time (FT).

Based on my previous research findings1, I suggest that just two trials of the 10/5 RJT are required before an accurate indication of your athlete’s reactive strength can be obtained. Reactive strength performance is calculated using the reactive strength index (RSI) obtained from the average of the best five rebound jumps (see Figure 1 for illustration). The idea of limiting the data to just the best five jumps came from a study2 that suggested reduced reliability in RSI scores likely arose from the high variation in GCTs possibly associated with the inability to control loading forces during repeated ground contact.

 

A comprehensive three-part review of RSI has recently been completed by Eamonn Flanagan (@EamonnFlanagan) on the Train with PUSH blog series, in which he discusses different options for RSI testing and the reason the 10/5 RJT test is “fast becoming his preferred reactive strength test.” In comparison to the classic RSI, the 10/5 RSI offers the opportunity to evaluate repeated stretch-shortening cycles (SSC) functioning under very short GCTs. This may be more specific to more cyclic movement sequences that demand the ability to repeatedly pre-activate muscles prior to each ground contact. In essence, better pre-activation ability allows for the passive elastic structures to contribute more to each foot ground contact, potentially making each step more metabolically efficient.

Practitioners do need to be aware that the 10/5 test may not challenge the degree of impact loading that players regularly encounter during plant foot forces while performing COD/agility tasks. It has recently been shown that athletes who can produce larger RSI scores at higher drop heights may have greater eccentric strength capacity, and thus be more equipped to tolerate and perform sporting actions that contain high eccentric stretch loads3. The 10/5 RSI has great potential for use as a regular monitoring tool due to its evident ability to evaluate both feedforward and feedback neural activity that coincides with events both before and immediately after foot ground contact.

Freelap USA: Deceleration is another quality that is seldom tested properly. Could you go into ideas that make sense for those in field or court sports? While agility/COD (change of direction) is never a pure strength quality, the capacity to handle forces is important for injury reduction.

Damian Harper: With developments in GPS/inertial sensor tracking technology, we are only now starting to realize the real significance of deceleration to sports that involve random intermittent dynamic movements. Although previous coaching literature⁴ raised issues about the lack of attention given to deceleration, unfortunately, from an experimental research perspective, the skill of deceleration still remains a forgotten factor. This statement can be appreciated when you look at the overwhelming focus and attention that has been given to understanding the determinants of an athlete’s acceleration capabilities. The increasing rate of injuries, despite clear advancements in training interventions, could have likely arisen due to athletes with heightened acceleration and maximum speed capabilities not being equipped with the correct resources to reduce such high forward momentums.

With such a lack of research devoted to understanding the complexities of deceleration, our training of this skill will remain sub-optimal/coincidental. A discussion about the physical/technical qualities needed is beyond the scope of this interview, but hopefully through my Ph.D. studies we should have some interesting information out soon that will start to bring some perspectives to this topic.

While we have recognized protocols and critical measurements identified for the assessment of maximal acceleration and top speed capabilities (e.g., horizontal force production), the measurement of deceleration is currently concealed within more traditional change of direction assessments. Sophia Nimphius is currently doing some excellent work that is challenging our current measures for COD performance. From current COD research, two important observations can be made that highlight the criticality of deceleration:

1. When entrance velocity into a COD or the angle of COD increases, the braking and loading demands become more challenging. Consequently, substantially greater quadriceps and hamstring activation is required (levels of EMG activity superseding that of linear sprinting)⁵.
2. Athletes who can apply greater posterior braking forces in the steps prior to COD have been shown to have superior COD ability⁶.

A third, perhaps not considered, observation is that tests that evaluate COD may not be creating events that challenge maximal deceleration capabilities. Therefore, whether the assessment of deceleration should be completed during a COD task remains questionable. I have devised a protocol that specifically isolates the deceleration component. Here, a rapid linear deceleration is performed following a maximal acceleration (ADA: acceleration-deceleration ability).

This test format is also a commonly used drill in team sport training to work on the skill of decelerating. Colleagues and I have used this drill to good success this year, to expose elite girls’ soccer players to regular doses of peak speed running and linear deceleration forces. This is something I picked up from Matt Reeves (@matt_reeves_ss), the head of fitness and conditioning at Leicester City Football Club, who called it the “Runway”—i.e., take off (accelerate), maintain speed, reduce speed (decelerate), and land the plane smoothly!

Although there is no compelling evidence yet, it is possible that players capable of higher rates of deceleration possess higher eccentric strength capacities7, which allows them to tolerate substantially higher impact loads. Essentially, this could be a protective quality that helps to reduce cumulative tissue damage, and therefore maintain overall movement efficiency and performance. For example, think of a player with a low deceleration ability having to quickly and unexpectedly brake. It is likely that impact forces will exceed the load absorption and force production capacity of certain structures, resulting in increased tissue overload and an increased chance of injury occurring. The use of GPS and inertial sensors, along with accurate measurement of center of mass (COM) velocity that can be obtained with radar/laser devices and/or high speed video timing, offers new opportunities in the field to gain more comprehensive insights into a player’s deceleration capabilities.

Freelap USA: American football has some similarities to rugby, where power from concentric strength is very common. Can you talk about how simple eccentric strength is important for ACL injury reduction? Any suggestions on what field and weight room solutions can help athletes as they gain muscle mass?

Damian Harper: First, a greater amount of research on the movement and loading demands of different positions in American football is clearly needed. There is evidence from a number of sports, including rugby, that habitual training and competition workloads can lead to low eccentric-to-concentric strength ratios, which could be corrected by targeted training interventions8,9. A recent study¹⁰ quantifying the competitive movement demands of American football provides unique insight into the position-specific running demands (see Figure 2).

 

From this data, it is easy to interpret that exceptional acceleration and deceleration skills are required. Since acceleration and deceleration involve such high mechanical loads, it is also not surprising that players with some of the highest frequencies of these movement actions also suffer the highest percentage of anterior cruciate ligament (ACL) injuries¹¹. These can have a severe negative impact on the career and livelihood of these athletes¹². For those readers not accustomed to some of the amazing acceleration-deceleration capabilities (see Video 2) of these athletes, I recommend that you scroll through the twitter feed of Ross Cooper (@GorillaMyscles) and read some of the in-game player movement evaluations that Shawn Myszka (@MovementMiyagi) completes on the Football Beyond the Stats blog.

Video 2: Acceleration and deceleration involve high mechanical loads, so it is not surprising that players with some of the highest frequencies of these movement actions also suffer the highest percentage of anterior cruciate ligament (ACL) injuries¹¹. This video shows an example of these amazing acceleration-deceleration capabilities.

These extreme dynamic braking impulses are clearly critical for elite level performance in the NFL, but are also very high risk events that could incite ACL injury¹³ (i.e., a body position where the COM is posterior to an extended lead leg that is applying a very high braking ground reaction force).

So back to the question: Can you go into how simple eccentric strength is important for ACL injury reduction? First, some of my recent research findings have found that high unilateral eccentric quadriceps strength is required to rapidly decelerate in less distance and time¹⁴. This is an interesting finding, and suggests a training intervention that focuses on eccentric overload of the quadriceps will help athletes to produce significantly greater braking and propulsive forces¹⁵, while also reducing injury risk and severity¹⁶.

From an injury-reduction perspective, such high eccentric quadriceps strength could increase the chances of anterior tibial translation if not accompanied by sufficient hamstring strength—again, another mechanism regularly reported for ACL injury risk. Therefore, a well-rounded strength-training intervention is required that specifically targets eccentric strength capacities of all quadriceps and hamstring muscles. This conclusion agrees with work done by Matt Jordan¹⁷ with elite alpine skiers, which found deficits in quadriceps and hamstring maximal and explosive strength in ACL-reconstructed knees.

Additionally, a weight room solution that conventional training interventions do not seem to consider deeply is what loading strategies may optimally facilitate tendon adaptation. It may be that certain tendon adaptations may further facilitate enhanced attenuation of the shock forces experienced during foot ground contact and serve to further protect muscle fibers from damage. Most importantly, increased strength capacities need to be transferred to increased exposure to on-field dynamic skill-based practice. For instance, by improving a player’s deceleration skill, the capability to regulate the magnitude and orientation of foot ground interactions will be enhanced. This will result in more-efficient force application, while also reducing external mechanical load.

Freelap USA: A study on leg muscle volume and acceleration came out recently. What are your thoughts on the value of that information for coaches on the field or in the weight room? Can we apply this information or is just food for thought, in your opinion?

Damian Harper: Part of the title of that study, “Adding muscle where you need it,” first caught my attention. (The full paper can be requested from the author at that link). Following the title, some of the questions posed in the introduction seem really interesting:

1. What is it that allows sprinters to generate such high velocities and accelerations?
2. Are hypertrophy patterns uniform in sprinters? Hypertrophy in some muscles could impair, rather than enhance, sprint speed.

Using MRI, 35 lower limb muscles of a group of 15 NCAA sprinters (some of whom also competed in jump, hurdle events, and sprint distances up to 400m) were scanned for muscle volume and compared to a group of 24 healthy, recreationally active, but non-sprint individuals. This was a novel study, with the possibility of providing a unique insight into the potential muscular strategy used by sprinters, and the information could provide new considerations for coaches working on developing sprint performance.

As you would expect, when normalized to body size, the sprinters had significantly larger knee and hip muscles, but surprisingly only the tibialis posterior was larger within the ankle muscles. When we take a deeper look at some of the specific muscles, the rectus femoris had the largest effect size difference of all muscles examined (d=2.6), while the semitendinosus (medial hamstring) contributed the largest effect size (d=2.6) and percent difference (54%) of the hamstring muscle group. These findings coincide with the significantly increased EMG activity of the semitendinosus compared to the biceps femoris observed during the middle swing phase (maximal knee flexion to maximal hip flexion) of near maximal velocity sprint running when a complex neuromuscular coordination pattern appears to occur. This suggests that this muscle plays an essential role in the control of hip flexion and knee extension under high load conditions¹⁸.

It seems a high eccentric strength capacity is especially required in the semitendinosus since just a small reduction in force output and negative work of this muscle may result in increased demand on the bicep femoris, which is less suited to tolerating high eccentric loads¹⁹. This implies that exercises that specifically target the medial and lateral hamstring muscle groups should be included, with particular focus on exercises that target eccentric strength at long muscle lengths and when the hip is flexed. For example, the razor curl (see Video 3) has been shown to create greater activation in the semitendinosus than the biceps femoris, with dynamic hip movement also contributing to simultaneous activation of both gluteus medius and maximus²⁰. Furthermore, some great work has recently been done by Dr. Anthony Shield’s hamstring research group, which has demonstrated that hip extension exercises more selectively activate the lateral hamstrings, whereas knee flexion-oriented exercise preferentially recruits the medial hamstrings²¹.

Training should include exercises that specifically target the medial and lateral hamstring muscle groups, with particular focus on exercises that target eccentric strength at long muscle lengths and when the hip is flexed20.

Finally, the last two observations I would like to make from this paper are:

1. Some muscles not so readily researched may have significant implications in high-speed running and warrant further research. For example, the gracilis, sartorius, and adductor magnus had some of the largest differences in muscle volume.
2. Careful consideration should be made to where muscle mass is added! For example, it has been suggested that a higher hamstring muscle mass relative to quadriceps muscle mass may be advantageous for sprinters²². This may also be the case in the ankle musculature, where higher muscle volumes may increase the mass of the limb, subsequently increasing swing heaviness and impairing sprint-running performance.

Freelap USA: Speed testing is important to see how training is transferring to core linear speed. Can you get into the details of the best protocol to keep the data clean and honest?

Damian Harper: I am not sure there is one given protocol that could be advised here, since some aspects of the protocol would likely change depending on the type of sport you are working with. For example, consideration should be made to standardized starting positions and signal methods. In American football, the measurement of the 40-yard dash is routinely assessed with a three-point stance; in soccer, it’s a standing static start/ flying start, and a block start in sprint events²³. Within each of these starting positions, timing could then be initiated with reaction (audio sensors, pistol) or be self-selected (recorded via foot/hand pressure sensors, photocells, or movement via video, radar/laser, or GPS/Inertial sensors).

These considerations are vitally important because different starting positions and measurement approaches can be combined to generate large absolute differences in sprint times²³. In addition to these considerations, other extraneous variables such as environmental factors, clothing and equipment, footwear, and running surface should also be considered. For a complete overview of these methodological and practical considerations, readers should consult “Sprint running performance monitoring” by Thomas Haugen and Martin Bucheitt.

Now, given that just 0.04 to 0.06 seconds can represent a distance of 30-50cm and be critical over 20m in team sports²⁴, it is essential that coaches can obtain data that can detect very small changes in performance enhancement. It is critical that practitioners monitoring speed on a regular basis know the noise typical error (TE) and smallest worthwhile change (SWC) for each measurement being used (e.g., 10m time, 20m time, max velocity, etc.) for the specific population group they are testing, to allow an informed decision on whether changes are real. It is also recommended that TE and SWC be calculated between days to account for possible variations in test performance.

Using this approach and a single-beam timing system (Brower Timing Systems) a recent study illustrated that, despite 10m, 20m, 30m, and 40m split times having good reliability (3.1%, 1.8%, 2.0%, and 1.3% coefficient of variation respectively) in rugby league and union players, the TE was consistently greater than the SWC, making each split time only “marginally” useful²⁵. Since single-beam timing systems have been shown to have less accuracy than dual-beam timing systems due to inherent problems associated with triggering of the beam (swinging arms, lifting knees), this highlights the importance of careful consideration to the measurement device being purchased, and also careful consideration to the other extraneous variables previously mentioned.

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References

1. Harper, D.J., Hobbs, S.J. & Moore, J. (2011). The ten to five repeated jump test: A new test for evaluation of lower body reactive strength. BASES 2011 Annual Student Conference. Integrations and Innovations: An Interdisciplinary Approach to Sport and Exercise Science. 2011 April 12-13; Chester, United Kingdom.
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