Force-Velocity: Relationship and Application

 

February 27, 2018 update: This post has been refreshed by Cedric Unholz to provide more up-to-date information and better communicate the practical applications of the force-velocity curve

 

Every sport imposes demands that exist along a spectrum of both force and velocity output. For example, football linemen need to generate large amounts of force to hold the line of scrimmage against their opponent but do not need to accelerate over long distances in a typical play. Soccer wingers, on the other hand, require exceptional repeated sprint capabilities to blow by defenders and exploit space, but do not require the same amount of absolute strength that football linemen do. As these examples highlight, it is crucial to understand the specific physiological demands of a sport /specific positions, and how training must be tailored to prepare an athlete for these demands. These needs also help highlight which relative qualities are of greatest importance to emphasise depending on goal and training phase.

The Force-Velocity curve (F-V curve) is a foundational model demonstrating the relationship that exists between the variables of force (mass x acceleration) and velocity (displacement/time) and lends itself well to conceptualising weightlifting prescription. In simplest terms, this model outlines that as load relative to a person’s 1-repetition maximum (1RM) increases, movement velocity decreases. If a higher movement velocity is desired, the relative load must be reduced.

There are however further considerations that must be taken into account depending on training goal. Power output is a product of multiplying force by velocity (Power = Force x Velocity), and improving this quality is a common training goal. Moving up or down the F-V curve manipulates this equation, producing distinct changes in stimulus and muscle recruitment profiles. Choice of load prescription (and by extension, movement velocity) therefore allows specific explosiveness qualities to be targeted (e.g. strength-speed vs. speed-strength). If applied appropriately, working in any of the curve’s ranges can also help improve an athlete’s rate of force development (RFD) which is a measure of how fast an athlete can apply force against a given load. A crucial requirement for improving this ability is the effect of intent – athletes must strive to produce maximal output against a load in every repetition to achieve the desired outcomes. Maximal intent can be encouraged through a variety of means, ranging from creating excellent training environments to the use of velocity-based training (VBT) technology. Specific feedback systems such as the Velocity Loss Cutoff (VLC) feature of the PUSH Band are helpful tools that ensure an athlete is performing lifts in the desired manner, and achieving optimal stimulus thresholds.

THE FORCE-VELOCITY CURVE

For ease of understanding we can break the F-V curve into 5 zones, each representing components of output emphasis using weightlifting as an example (Figure 1). The intensity brackets defined in the diagram are general ‘rules of thumb’ that provide a conceptual model, with overlap existing between neighbouring segments. The F-V curve relates to outputs generated during the concentric portion of a movement/exercise (e.g. the upward phase of a squat or bench press).

Figure 1. A force-velocity curve with specific training zones denoted

Zone 1: Maximum Strength (90-100% of 1RM):

  • Emphasis = Force Production against very high relative loads
  • Lift will be very heavy
  • Force output generated will be very high
  • Velocity of the lift will be very slow

Work in this area will target/develop the maximal amount of force an athlete can produce. Whilst absolute movement velocity will be slow, it is vital to ensure maximal movement intent in order to help aid successful lift completion and desired muscle/neural recruitment profiles.

Zone 2: Strength Speed (80-90% of 1RM)

  • Emphasis = Explosive power production against high relative loads
  • Lift is heavy
  • Force output generated will be high
  • Velocity of the lift will be slow
  • Power = FORCE x Velocity

This zone allows for a combination of substantial force outputs (though lower than those in Zone 1) and increased movement speeds when compared to maximum strength work. Because the relative loading intensities are still quite high, work in this zone targets power development with an emphasis on force production which is why this is termed ‘strength-speed’.

Zone 3: Peak Power (30-80% of 1RM)

  • Emphasis = Velocity output against high to moderate relative loads
  • Lift is light
  • Force output generated will be low
  • Velocity of the lift will be high
  • Power = Force x VELOCITY

There are many variables that determine peak power output and each athlete has a different power profile. The recommended loading range for eliciting peak power is therefore very broad (30-80% of 1RM). It is important to note that some studies have even found peak power values to occur at loads as low as 0% of 1RM.

Zone 4: Speed Strength (30-60% of 1RM)

  • Emphasis = Explosive power production against moderate to low relative loads
  • Lift is light
  • Force output generated will be low
  • Velocity of the lift will be high
  • Power = Force x VELOCITY

Work in this bracket creates lower absolute force outputs but significantly higher movement velocities compared to Zone 2. As the relative loading intensities are lower, this zone targets power development with an emphasis on velocity production which is why this is termed ‘speed-strength’.

Zone 5: Speed (<30% data-preserve-html-node="true" of 1RM)

  • Emphasis = Velocity output against very low relative loads
  • Lift is very light
  • Force output generated will be very low
  • Velocity of the lift will be very high

This zone allows for the highest movement velocities and the lowest force outputs compared to the other zones. Similar to peak power there can exist a large amount of individual variation here as to the loads that elicit the fastest speeds. As mentioned previously some individuals may actually produce their peak power output in this zone as well.

BUT I ALWAYS LIFT HEAVY…

Stimulus is a signal for response, and the body adapts to what it is regularly exposed to. Working solely in one portion of the F-V curve can lead to large improvements and specific recruitment skill development relative to that loading spectrum. This may however limit an athlete’s global strength/power profile especially in sports where a variety of attributes and qualities must be developed. As an example, focusing exclusively on maximum strength may help increase absolute force production over time, but overemphasis can also lead to decreases in explosive muscle contactile properties (Figure 2). Similarly, assigning too much focus on low load/high velocity lifting may develop certain movement speed qualities, but can also result in stunted maximum force output capabilities (Figure 3).

image

Figure 2.

image

Figure 3.

The most common solution to the above is the use of a mixed methods or ‘conjugate’ approach. In this system concurrent training of complementary training elements (e.g. maximum strength and aerobic restoration work) are arranged in successive training blocks. Training emphases and volumes are then progressed/adjusted over time relative to an individual athlete’s needs. This allows the sequential development of multiple qualities at one time, whilst mitigating the detraining of non-emphasised training elements. In terms of an athlete’s F-V profile we are therefore able to achieve two major primary outcomes (Figure 4):

  1. Increase the amount of force an athlete can produce at any given velocity, shifting the athlete’s F-V curve upwards.

  2. Increase the speed at which the athlete can move a given absolute load in his/her lifting range, shifting the athlete’s F-V curve to the right.

image

Figure 4.

Understanding each segment of the F-V curve and how it pertains to training is an imperative skill for any S&C coach. Successful long-term training development relies heavily on the appropriate implementation of these zones, which must be applied at the correct times relative to the needs of the athlete/sport being trained for.

REFERENCES:

1. Siff 2004. Supertraining.

2. Cormie et al 2007. Power vs strength - jump squat training. Medicine & Science in Sports & Exercise.

3. Issurin 2011. New horizons for the methodology and physiology of training periodization.  Sports Medicine.