Beyond the Force Velocity Curve with Assisted Jumps Training

The sprinting and jumping events in Track and Field are dynamic activities that require great speed, strength, power, coordination, and control. Athletes can reach speeds in excess of 12 m/s during the 100 meters and in some cases over 11m/s prior to takeoff during the horizontal jumps. Tables 1 and 2 below illustrate the speed and force requirements of these events.

Speed is the single most important quality. In order to develop speed, you have to generate force and impulse against the ground (horizontal or vertical). As a training stimulus, the athlete ultimately needs to develop higher levels of force at higher velocities and in less time. Essentially, this means training across the force–velocity spectrum to target different mechanisms that influence overall athletic development. This combination of force and velocity training is often regarded as power training. Different aspects of the events require specific characteristics of power that, in turn, require specialized training stimulus. Power is not simply a single expressive ability, but is instead the sum of several different competencies.

Understanding the exact event requirements and characteristics of strength and power is essential for designing effective training programs. Specifically, research performed on the force/velocity curve has shaped many of the practices we follow today. We know that maximum power output is obtained when a particular combination of force and velocity is demonstrated. This notion has led us to develop training strategies focusing on two distinct areas: a) force output with no time restraints; and b) force output with time restraints. The combination of these methods constitutes common ground among many of today’s leading experts.

The sprinting and jumping events utilize extremely specialized force/velocity requirements. The limiting factors lie in the neural and muscle-tendon capabilities for producing maximum force in minimum time. Therefore, it is the velocity component of applied force that requires specific attention in the training program. As power potential is determined to a high degree by maximum strength levels, it would be irresponsible to suggest that developing high velocity force in isolation will produce long-lasting improvements in overall power output. Likewise, an increase in maximum strength will not automatically improve power’s velocity component. This means that we must take a closer look at traditional power training methods to ensure their effectiveness when developing the qualities of sprinters and jumpers.

Traditional Methods of Power Development

When accelerating to develop high horizontal speeds or when generating vertical speed in the take-off phase of the jumps, an athlete creates impulse against the ground. This requires athletes to generate large forces in a limited amount of time (as outlined in Tables 1 and 2). Strength and conditioning specialists often refer to this quality either as Power or exhibiting high Rate of Force Development (RFD). These terms are often used interchangeably, but they are subtly different. We will try to differentiate between these terms here and give them some context.

Power is defined as the rate of performing work.

Power = (Work Done) / Time

as Work Done = Force x Displacement,

Power = (Force x Displacement) / Time

Therefore,

Power = Force x Velocity, or Power = RFD x Displacement.

When in contact with the ground, the athlete generates power by developing high levels of force in short duration (RFD) and displacing his/her center of mass through an appropriate range. For any given athlete performing a dynamic movement where the center of mass is being displaced, these terms may be used interchangeably. However, in isometric contractions where there is no displacement then there will be high levels of RFD but zero power. This is worth bearing in mind when considering different types of muscle contraction and various training modalities with respect to force application and movement velocity.

Jump and power development often incorporates combinations and variations of maximum strength protocols (some of which may be isometric), ballistic training methods, and plyometrics. We will take a closer look at each of these components.

Maximum Strength

Maximum strength development is an important foundation for power output improvement. Strength is the capacity of the skeletal muscle to produce force and a given velocity. Maximum strength is enhanced through the use of weightlifting exercises using heavy loads of 90-100% of the 1 Rep Max (1RM). Dynamic exercises such as Olympic weightlifting variations performed at such loads develop explosive strength qualities such as maximum RFD. Isometric contractions and less dynamic exercises such as squatting target high levels of muscle fiber recruitment, where contraction velocities are high but movement speed is low. These qualities are required to overcome inertia and are key characteristics for starting strength. However, the takeoff velocities seen in jumping events and during maximum velocity sprinting require not only high levels of recruitment, but also high speeds of contraction. Such neural activation is highly correlated with improvements in fast force production.

Another possible drawback of maximum strength development is that selective fiber recruitment is not possible, due to the low velocity component related with this method. Maximum strength development requires the recruitment of both slow (type 1) and fast (type 2) muscle fibers, and is not recommended in isolation for long periods of the training year. As a result, other forms of power development are more suited for high-end speed/power athletes.

Ballistic Training

The velocity and reactive components of power are the most difficult to adapt through training. Special training targeting these abilities needs to be a constant throughout the training program. This means that, from Week One of preparation, the athlete must be exposed to specific stimuli that develop high-speed neuromuscular qualities. Performing explosive weightlifting and medicine ball exercises is a major advantage for this reason, with an athlete training at maximum intensity with loads of 10-50% of the 1RM to enable selective recruitment of fast twist muscles fibers and enhanced muscular firing rates. Exercises including weighted jumps, Olympic weightlifting movements, and implement throwing are excellent methods of developing specific strength with a velocity focus.

Reactive Strength

The most specific quality needed is reactive strength. Force application in the sprinting and jumping events can be characterized by a rapid eccentric muscle action followed by a concentric muscle action. This can also be described as a muscular stretching phase followed by a muscular shortening phase, otherwise known as the stretch-shortening cycle (SSC). An efficient SSC is characteristic of the fastest human movements.

Stretch-shortening cycles are present in every muscle within our body. There are many stretch-shortening processes occurring during every sprint stride and takeoff action. A single jump in a vertical plane consists of stretch-shortening cycles within the core musculature, hips, quadriceps, hamstrings, glutes, gastrocnemius, and so on. Priority when training for reactive strength is placed on the stretch reflex capabilities of the lower limbs and core as they primarily influence the ability to sprint and jump.

We aim to achieve several distinct outcomes during the ground contact phase. Ideally, ground contact time is short, horizontal and vertical impulses are high, and the breaking forces are low. There are several factors at play that must be addressed via the development of reactive strength. Muscles and tendons are designed to store and release energy during fast pre-stretches and subsequent shortening muscle-tendon actions. Tendons are considerably better at storing energy than muscles. In particular, the Achilles tendon is an essential target of all lower body plyometric activities.

Traditional plyometric training enhances the stretch reflex mechanism, increases tendon stiffness, and targets the velocity component of rate of force development. The length and stiffness properties of tendons play a critical role in the high velocity force capabilities of the stretch reflex mechanism. Repetitive stiffness jumps, depth jump variations, and bounding exercises are popular methods of plyometric training. Focus during such activities should be placed on the pretension prior to ground contact and the speed of the stretch reflex.

Training methods aim to overload certain structures to produce greater training effects. While overloading strategies for developing low velocity power are obvious, it is not so obvious how to overload the other end of the spectrum. While the most intense variations of plyometric exercises provide overload regarding impact forces and stretch reflex, they are not able to minimizing contact times beyond what is naturally possible. It is therefore important to understand that overloading the velocity component, and specifically the time programs within the neuromuscular system, is not possible during traditional means of training. The use of an external support system that facilitates ground contact times and concentric muscle actions provides an opportunity to target such time programs.

Assisted Jumps and Overspeed Training

The purpose of assisted jumps training is to expose the central nervous system to faster time programs stored with the muscle-tendon systems. Assisted jumps training requires an external support system in the form of an overhead bungee cord or elastic bands. The athlete is attached to the overhead bungee and their body weight is strategically decreased while they perform various plyometric exercises. These conditions make it possible to achieve such shortened muscular firing rates, ground contact times, and time programs within the central nervous system. Assisted jumps training can be comparable to a more commonly used speed development method called overspeed training.

Overspeed training for sprinting elicits similar neural and muscular responses to those found with high-velocity jump training. The premise behind overspeed sprinting is that having an athlete sprint at supramaximal velocities will enhance CNS firing rates, reduce the inhibitory mechanism within the neuromuscular system, and increase stride frequency. Overspeed training enables an athlete to experience sprinting speeds and reduced ground contact times not otherwise possible via traditional means.

Commonly used methods of overspeed training include downhill sprinting and sprinting while being pulled by a bungee cord device. As with assisted jumps training, it is suggested that overspeed training enhances timing mechanisms and creates new motor programs. A variety of studies have found that overspeed has both an acute and chronic effect on increased horizontal velocity.

Assisted Jumps Training Research

Assisted jumps training is far from a novel concept. Its use can be traced back to the 1970s, and perhaps even earlier. However, very little research and practical application of the method has been performed. Before discussing specific programming concepts, we will talk about some of the relevant research on the topic.

Giovanni Cavagna was the first to study the effects of assisted jumping. In a study for Aerospace Medicine in 1972, he demonstrated that jumping in low-gravity conditions (using a suspension device) decreased time of force production as compared to normal jumping conditions. Subjects using the assisted device demonstrated force output similar to that of non-suspended subjects, but in reduced time.

Yu Imachi of Japan emerged as the pioneer in the research of assisted jumps training. In an early study, 20 male high school volleyball players were divided into three training groups and tested on their vertical jump height. After a 10-week training period, the assisted jumps training groups using protocols of minus 10% and minus 20% body weight had improved vertical jump performance significantly greater than that shown by participants in the group performing plyometric training under normal conditions. Each subject performed 10 maximal effort vertical jumps with 15 seconds of rest between each jump, three times per week. A similar study was performed using female athletes and showed similar results.

In a more recent study, Imachi compared takeoff velocities and force production of assisted jumping with that of free jumping exercises. The results indicated that assisted jumps training did not improve the maximal force production of the athletes. Instead, the improved jumping ability was a result of greater takeoff velocity.

Brazilian jumps specialist Nelio Moura is perhaps the best-known contemporary proponent of assisted jumps training. Although little is known about his protocols for using the method, there are several videos of Olympic champion long jumper Irving Saladino using the device in training. I have had several email conversations with Nelio regarding the method and he mentioned that he uses it all year and with athletes of all age groups. Nelio has had incredible success over a long time span and we should highly respect his opinion on such training.

Programming Assisted Jumps Training

When performing assisted jumps, it is important to realize that the increased jump height is not an acute effect, as you are being assisted by elastic energy. Let us address how ‘reducing’ body weight works in reality. It is true to say that the stretch–recoil from the bungee will indeed lead to greater vertical displacement of your center of mass. Consequently, during the landing phase of each jump you will experience a greater stimulus for increased forces (and thereby passive eccentric loading), which is initially directed in the Achilles tendon. Following this, the bungee will progressively develop tension and dampen the loading around the knees and hips as they respond to the greater landing forces.

This “assistance” means that the knees and hips do not flex excessively and are able to develop sufficient eccentric musculotendinous loading to promote a faster coupling time and maintain a respectable ground contact time. This moderate amount of damping through the knees may allow you to more safely perform repetitions with reduced risk of jumpers’ knee. Over the course of a training phase you will adapt to increased passive landing forces (but undoubtedly still lower than actual impact forces in the long, triple and high jumps), while still generating high (but not excessive) eccentric loads in the Achilles and Patellar tendons. This gives the stretch reflexes the sensation of an appropriate level of overload and fast coupling time into the concentric phase.

Successful training programs must adhere to a combination of principles relating to readiness and response. It is therefore impossible to single out a particular training method or exercise protocol when determining performance improvements. However, based on research and case studies performed by ourselves and other jumps and sprint coaches, we can confidently state that Assisted Jumps Training is a method that fits naturally within the scheme of a program. It can be programmed much like other highly intense plyometric exercises.

Due to the velocity component, it is best grouped with maximum velocity development such as fly sprints or activities of that nature. We recommend implementing the method after the athlete’s general preparation phase and using it throughout the competitive season. The neural demands make it a potential primer exercise during competition weeks; however, we would reduce volume considerably during this time. Potential exercise choice is limited to those in a vertical plane; otherwise, regular plyometric choices can be utilized.

Logistics and the Assisted Jumps Device

If you are considering making your own assisted jumps device, the most important factor is the ability to adjust the bungee cord tension. Different athletes will require slightly different adjustment settings when trying to achieve a specific reduction in body weight. We have used devices that are attached to a pulley system on a wall that can be easily adjusted. Although this is a great setup, it is only practical if you plan on creating a semi-immovable device and have a permanent space for it.

The parts needed for a device similar to this include a basic bungee cord, a belay system, a carabineer, a rope, and a harness. We recommend the device that we currently use, which is very simple and almost made specifically for this purpose. This assisted pull-up device, found in a local sports store, is easily moveable and very simple in design. Simply attach a harness and it works perfectly as an assisted jumps training device.

It’s Time to Add Assisted Jumps Training to Your Training Program

Heavy resistance training develops muscular strength and rate of force development properties that can increase the potential for power production. Plyometric and ballistic training impact the velocity component and the efficiency of the stretch-shortening cycle. Assisted jumps training is able to create new time programs with the central nervous system enhancing fire rates and other intramuscular coordination qualities. Understandably, research on assisted jumps training has been very limited up to this point. While we find great value in case studies, we also understand their limitations. However, from the findings we do have, it seems safe to assume that optimal training for speed and power should incorporate all three of these training methods.

To date, the positive findings appear consistent and should lead to enough interest for coaches to implement this method into their training program—at the very least, for the sake of variety. Successful training methodologies often share similar, if not identical, characteristics. These include characteristics such as intensity, specificity, overload, heavy, light, slow, fast, short or long recovery, etc. Coaches understand exactly where these fit into their plan and there is little argument over their place. We program many facets of the training program across a wide spectrum, from non-specific to specific, slow and heavy to light and fast, static to dynamic, simple to complex, and more. We understand the need for variety and progression and, for the most part, we understand how the different training methods promote specific adaptation.

The discussion of strength development will always be a favorite pastime of coaches, but the speed and velocity components of movement and technical application clearly serve a far greater importance. With that being said, it is surprising that assisted jumps training and overspeed sprinting are not more widely used. If your reasoning is that it’s a time and logistics issue, that’s a poor excuse.

Assisted jumps training truly doesn’t require expensive equipment or fancy devices, and almost all facilities have the necessary space and ceiling requirements. Perhaps the reason for its exclusion is a lack of awareness. If you are obsessed with jump development, you will leave no stone unturned in your pursuit of higher heights and farther distances. We hope that this article will inspire you to at least research further and experiment, in the way that most training methods began their journey to acceptance and normalcy. Good luck!

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Nick Newman, MS, CSCC
Nick is the current Director of Scholastic Training at Athletic Lab in Cary, North Carolina. Before joining the Athletic Lab team, Nick dedicated 10 years to the study and application of the development of athletes ranging from pre-adolescent youth to the professional ranks. Nick earned his bachelor’s degree in Exercise Science from Manhattan College and later earned a master’s degree in Human Performance and Sport Psychology from California State University, Fullerton. Nick is a jumps and sprints specialist and, in 2012, he published his highly acclaimed book, The Horizontal Jumps: Planning for Long Term Development, which has been endorsed by several world-class speed and power coaches. Nick prides himself on his ability to teach and relate to athletes of all ages and levels. His passion and expertise in athletic development is second to none. Nick is a Certified Strength and Conditioning Coach, a certified Track and Field Technical Coach with the USTFCCCA, and a Sports Performance Coach with USA Weightlifting.

Dr Phil Graham-Smith, BSc, Phd, CSCS, CSci, FBASES
Phil is currently the Head of Biomechanics at the Aspire Academy of Sporting Excellence in Doha, Qatar. In addition to his academic career at Liverpool John Moores University and the Univerity of Salford, he was also the consultant Head of Biomechanics at the English Institute of Sport. He is an Accredited Sports Biomechanist and Fellow of BASES, a BOA registered Performance Analyst, and a Certified Strength & Conditioning Specialist (NSCA). He has over 25 years applied experience providing biomechanical support to UK Athletics, Aspire, and Qatar athletes and professional football and rugby clubs. His is also co-founder of ForceDecks, an intuitive system designed for strength, power, and asymmetry diagnostics in professional sport.

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