Wearable resistance training for speed and agility

Strength and Conditioning Journal Publish Ahead of Print DOI: 10.1519/SSC.0000000000000436

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Joseph Cleary Dolcetti,1 John B. Cronin,2,3 Paul Macadam,2 Erin H. Feser 2,4

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LILA Movement Technology, Kuala Lumpur, Malaysia

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AUT Sports Performance Research Institute New Zealand, Auckland University of

Technology, Auckland, New Zealand 3

School of Medical and Health Sciences, Edith Cowan University, Perth, Australia

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Exercise Science and Health Promotion, Arizona State University, Phoenix, United

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States

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Paul Macadam, AUT Sports Performance Research Institute New Zealand, Auckland University of Technology, Private Bag 92006, Auckland 1020, New Zealand, +64 99219999, +64 99219960 (Fax), [email protected]

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Wearable resistance training for speed and agility

No funding was received for this work.

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Copyright Ó 2018 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.

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Authors

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Joseph Cleary Dolcetti is a high performance conditioning specialist, CEO/Founder of LILA Movementechnology and creator of the Exogen Exoskeleton wearable resistance.

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John Cronin is a Professor in Strength and Conditioning at Auckland University of Technology, New Zealand, and an Adjunct Professor at Edith Cowan University, Australia.

Paul Macadam is a doctoral candidate at Auckland University of Technology, New Zealand.

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Erin Feser is the Director of Education at Noraxon USA, Adjunct Faculty at Arizona State University, USA, and a doctoral candidate at Auckland University of Technology, New Zealand.

Abstract

There are many training tools available to the coach for the improvement of speed and agility, this article discusses the use of wearable resistance (WR) and its place in the conditioning continuum. In terms of specific strength training and transference of adaptation to speed and agility, WR training is a bona fide contributor and can make a real difference to athleticism and competition performance. However, the utilization of

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WR training is embryonic, therefore the focus of the article is on enhancing

understanding and providing generic guidelines that can be translated across multiple

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movement patterns and sporting situations.

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Keywords: Sprint, change of direction, acceleration, neural, mechanical, overload

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Introduction Several training options are available to produce speed and agility adaptation, however this adaptation needs to be specific to the requirements of the sport and the athlete (1). Though non-specific training plays a role in certain phases of the periodized plan, the

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transference of non-specific strength and power, to speed and agility, is usually minimal at best, as a general strength phase is needed i.e. hypertrophic responses need volume and

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load. For example, Cronin et al. in reviewing the effects of increasing squat maximal strength on sprint performance, found that increases of 23% in squat one repetition maximum (1RM) were necessary for significant changes in sprint times (> -2%) in

untrained subjects (5). With closer scrutiny, there is little wonder that there is minimal transference of gym-based gains to speed and agility performance as most exercises lack the specificity needed for optimal transference. For example, some of the limitations of gym-based exercises/training are many exercises are performed bilaterally, whereas the

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activities of interest are principally unilateral. Most exercises are vertically oriented, and horizontal and lateral force production are somewhat forgotten, even though principal

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components of speed and agility. Moreover, exercises tend to be acyclic whereas movement in the field is cyclic, with exercises lacking velocity, range of motion,

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contraction type and metabolic specificity to the activity or sport of interest. Furthermore, movement is typically uni-planar, whereas movement in the field is usually multi-planar, and sport as a competitive outcome is multi-dimensional. Gym based exercises usually have little to no connection to the actual competition environment that affects the athlete’s mood, focus, perceptions and flow. How often have we seen an athlete with exceptional test scores and high predictability to perform well, fail to produce results in

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an actual competition?

Compared to the untrained athlete, making changes in well-trained and/or elite athletes is even more difficult, and requires creative programming from the practitioner (21). The

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importance of the principle of specificity in optimizing transference of training adaptation at the macro- to micro-myofibrillar level (3), would seem even more important for such

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athletes. One training method that enables such specificity for improving speed and

agility performance is WR training. WR training involves an external load being applied to segments of the body during movement, and is an example of the application of the concept of training specificity i.e. it is resisted movement training (9). WR has the potential to address the limiters to transference as described previously (e.g. lack velocity, range of motion, contraction type, metabolic specificity to the activity of interest and disconnect from the competition environment), and as such provides the focus of this

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paper. First, the reasons why WR may be a powerful training modality to improve speed and agility are articulated. Thereafter, how WR can be used to first coach and then train

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athletes is discussed.

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The Why of WR

In this section mechanical, neural and metabolic support for the use of WR is briefly introduced, the discussion elaborating on the overload that WR provides, and the efficacy of this technology as a training tool for improving speed and agility performance.

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Mechanical This section provides the reader with some understanding of the unique mechanical overload provided by WR, as compared to more traditional forms of training.

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High Forces – Different Means to the End A major focus of strength and conditioning coaches is improving the force capability of

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their athletes, given speed and agility are the result of the force produced against the

ground, it’s orientation and the time over which that force acts (4). To build the internal force capability of athletes, coaches generally require the athletes to overcome large external forces by lifting large masses, but the velocity of movement and associated accelerations are small (see Figure 1A). However, the use of WR recognizes that there are other ways to develop high forces via the use of light loads (grams as well as kilograms), and high movement velocities and concomitant accelerations (see Figure 1B)

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which for many sports, are likely more relevant to performance. For example, though heavier loads ranging 2-18 kg (3-30% body mass (BM)) have been used with weighted

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vests in sprints and jumps (6, 11, 12). When the loads have been attached to the limbs during sprints and jump, lighter loads of 0.5-3 kg (1-5% BM) have provided a sufficient

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overload resulting in significant changes to the variables of interest (10, 17, 20). Moreover, training at the velocity needed for performance is a necessary component to develop velocity specific changes in force production capabilities (15). The added benefit of this training is that it is movement pattern and movement velocity specific, unlike traditional resistance training (TRT) which utilises heavier, gym-based free-weight and machine exercises and are typically force dominant. Therefore, WR would seem a

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suitable choice for speed and agility development.

Insert Figure 1 about here.

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Understanding Rotational Inertia In contrast to studies which have attached the loads to the trunk using weighted vests,

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WR when placed on the limbs or in combination with trunk loading, provides a direct

rotational overload to that limb and therefore the proximal joints and musculature (14). This is unique and has high ecological validity given that linear motion is typically the product of rotational motion of the arms and/or legs. Therefore, rotational inertia is an important concept to consider when using WR, that is, the resistance of an object or in this case a limb, to rotational/angular motion. Rotational inertia is the product of the mass of the object and mass distribution in relation to the axis of rotation. This is

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represented by the formula I = mr2, where I is the rotational inertia, m the mass and r2 the

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distance from the axis squared.

An example of how this concept is applied can be shown with two different thigh load

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placements. A thigh with two loads of 200 grams each (400 grams total), A and B placed along the limb, one mid-femur and one at distal-femur can be observed in Figure 2. Because of the distal placement of B in relation to the axis of rotation (hip joint), this load placement the r variable in the equation increases resulting in greater rotational inertia, which equates to more muscular effort needed to accelerate and decelerate the limb. The question arises then, what is the magnitude of this inertia in relation to placement and the

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mass used? Table 1 depicts the increase in rotational inertia values for a thigh loaded at mid femur and distal femur for a 177 cm, 84 kg individual. As can be observed from the table, 2 x 200grams (400 gm) placed mid (4.73%) vs. distal-femur (12.1%) resulted in substantial increases in rotational inertia. So, in the case of the distal loading, there is

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~12% more muscular effort required to accelerate and decelerate the thigh for every step taken. Even though we are talking grams instead of kilograms, the movement specific

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overload on the neuromuscular system is both substantial and still barely understood.

However, what is clear is that a change in rotational inertia increases the kinetic output of the joint proximal to the location of the added load, and this affect is greater when the load is positioned more distally and when the load magnitude is increased (13). Moreover, previous research has found that extra mass on the thigh and shank appear to affect step frequency more so than step length, by increasing contact time and decreasing swing velocity (9). Vest loading on the other hand, seems to affect step length more so

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by increasing contact time, and decreasing flight time and therefore flight distance (9).

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Insert Figure 2 and Table 1 about here.

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Neural

Improving neural efficiency to enhance force capability and movement quality is another focus for the strength and conditioning coach. This is typically achieved by improving both intramuscular and intermuscular co-ordination. Developing intramuscular coordination involves improving motor unit recruitment, firing frequency, synchronization and reflex activity (8). It is widely acknowledged that this can be achieved via training

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that is heavy and/or explosive. Developing intermuscular co-ordination involves improving synergistic contribution, fixator involvement and co-contraction of antagonists. For this to occur training needs to be movement and speed specific and adaption for the most part is not transferable to other movements (18). As Poliquin

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proposed the issue with specificity is that the motions of these (TRT) exercises are too distant from the biomechanics of sprinting – you are training the muscles, not the

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movements (see Life change through Fitness website at https://

lifechangethroughfitness.wordpress.com/2011/11/01/good-read-on-sprinting-by-poliquincarl/).

Siff stated that all sporting movement is specific and goal directed (19). Therefore, the strength displayed in the execution of each movement needs to be specific and goal directed e.g. strength needs to be developed in the context of the speed and agility tasks

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of interest. Warren Young in a treatise of transferring strength and power training to sports performance wrote, “it appears that to maximize transfer to specific sports skills,

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training should be as specific as possible, especially with regard to movement pattern and contraction velocity. This type of training can be expected to enhance intermuscular

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coordination and ensure that muscles are “tuned” to any newly acquired force generating capacity. Adding a load to a sports movement would seem to be a suitable strategy to achieve this specificity, although the amount and direction of added resistance would need to be considered” (22). WR training provides such movement/context specific overload and in the author’s opinion is one of the best training methods to enhance intermuscular co-ordination for speed and agility performance.

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Metabolic Plisk and Gambetta (16) in a treatise on tactical metabolic training stated that from a practical standpoint, athletes are usually more involved in and enthusiastic about specialized, task oriented exercises/activities that have direct transfer to their competitive

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event. Once more, WR can provide such task or context specific metabolic overload, however, a concern might be that such overload increases the magnitude of the landing

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ground reaction forces and therefore increase injury probability. This has been shown not to be the case in jumping, running and sprinting research (6, 9, 11) as the effect of the additional mass, such as in vest loading, decreases the vertical displacement of the center of mass, which in turn reduces the effect of acceleration due to gravity and subsequent vertical ground reaction forces.

Though no research to the knowledge of the authors, has reported the metabolic costs of

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WR during sprinting and agility activity, there are a few studies that have reported the energy expenditure during running, which can give insight into the magnitude of the

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metabolic overload that WR training can provide. In summary, trunk loading on average increased energy cost by ~2.5%, 4.2% and 8.5% for added loads of 5%, 10% and 15%

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BM respectively (7). This energy cost is magnified considerably when extra mass is added to the lower extremities. For example, Martin (13) reported 5 to 10% increases in energy cost for loads less than 1 kg (