Rapid Rate of Force Development

By Kevin Neeld

For www.EliteFTS.com

 

Rate of force development (ROFD) is probably the most important and under-recognized area of applied science pertaining to strength training and athletics. ROFD essentially refers to the speed at which force can be produced. Aside from those sports requiring very precise movements (such as gymnastics and ballet), I can’t think of a single example in athletics or lifting that wouldn’t benefit from a faster ROFD. A faster ROFD results in quicker, more explosive movements and gets the bar moving sooner.

Let’s take a look at an example. Let’s say two people (lifter A and lifter B) are attempting a 500-lb deadlift. Both are capable of producing 500 lbs of force, but lifter A has a significantly faster ROFD. It may take lifter A two seconds to produce enough force to get the bar moving off the floor and four seconds to lock it out at the top. Lifter B, with an inferior ROFD, takes four seconds to get the bar moving off the floor and six seconds to get it to his knees. He reaches failure before locking out at the top.

As with most things in strength training, there’s a neural explanation. On a neural level, ROFD means that typically high threshold motor units (MU) are recruited at an earlier absolute time. I emphasize earlier absolute time as the relative time defined as the recruitment relative to other motor units (recruitment order). It stays the same in slow and fast ROFD contractions (1). Slow twitch MU are recruited prior to fast twitch MU.

Despite popular belief, fast twitch MU are rarely (essentially never) active unless all slow twitch MU are active, and even if this was possible, it would not be desirable. Slow twitch MU produce force, and fast twitch MU produce more force. Together, slow and fast twitch MU produce more force than either could individually. In both types of MU, decreasing the absolute threshold time has significant implications on the amount of force produced.

High threshold MU can produce more force per stimulus than lower threshold MU. Therefore, when high threshold MU are active along with low threshold MU, more absolute force can be produced. Greater recruitment in a shorter amount of time increases the intramuscular tension more rapidly.

Without a doubt, you know that high threshold MU produce more force than low threshold MU. For what it’s worth, in an exercise neuroscience class that I took as a graduate student, we were taught that on average slow twitch MU produce about 5 grams of force per MU, and fast twitch MU produce about 20 grams of force per MU. However, I couldn’t find a source for that so take it with a grain of salt.

While you may be familiar with the idea of intramuscular tension, you may not have a clear understanding of its role in the initiation of movement. Typically, when the contractile elements of a muscle begin to produce force, the elastic elements of the muscle begin to lengthen. However, movement does not occur yet. It is not until the elastic elements of the muscle stretch sufficiently to increase the stiffness of the muscle that movement occurs.

The classic example is stretching a rubber band. When the rubber band is loose, the stiffness expressed across it is quite low. When the rubber band is stretched taut, the stiffness expressed across it is much higher. As a result, the time to reach peak force is dependent on the time course of this interaction between the contractile and elastic elements of a muscle. By having more motor neurons innervating the muscle fibers of any given muscle fire together, the stiffness of these elastic elements can be increased more rapidly, allowing a shorter latency between the initiation of force and the initiation of movement. This also allows subsequently recruited MU to capitalize on the stiffness created by MU that have been previously activated, increasing the total muscular force rapidly.

Thinking of our deadlift example, this is very important for completing a maximal effort movement. This is less important in movements that follow an eccentric-transition-concentric movement pattern. It has been established that concentric strength is less than eccentric strength. As a result, the ability to complete a lift is typically limited by an individual’s concentric strength.

So why would a rapid rate of force development be less beneficial for a squat or bench press than a deadlift? Results from research involving preceding a concentric contraction with an eccentric or isometric contraction has illustrated that the force at the beginning of the concentric contraction is significantly higher than a concentric contraction alone (2–5). While most people think of this as an illustration of the effect of the stretch shortening cycle, it is more likely due to the increased time for activation (5). This is supported by the fact that increasing the amount of negative (eccentric) work results in no increase in positive (concentric) work (4). Because both squat and bench press movements involve an eccentric contraction preceding a concentric contraction, there is ample time for activation and tension to rise. With that said, there aren’t any negative consequences if you improve your ROFD in these lifts. In competitions that require a pause at the bottom, a faster ROFD will probably still help as well. 

The majority of the research on ROFD involves ballistic or rapid contractions. The findings are relatively consistent. Recruitment thresholds decrease as ROFD increases. One study found that three times as many MU were active during a ballistic contraction compared to a slow ramp contraction (1). A logical deduction from this is that most, if not all MU, may be recruited during ballistic contractions at about 33 percent of maximum force. However, this is not the same in all muscles because muscles with a greater proportion of slow twitch MU, such as the soleus of the lower leg, have a greater decrease in recruitment threshold compared to muscles with a greater proportion of fast twitch MU (6).

Another interesting study found that preceding a ballistic movement with a low level contraction significantly reduced the rate of torque development (7). This seems like a bad thing because the MU are in a refractory period and aren’t able to produce force at the initiation of the movement. However, because certain MU are already active, the amount of force left to be produced is significantly less than if the contraction began from rest. The observed decrease in rate of torque development is probably a simple illustration of a ceiling effect.

The authors also noted that in cases where there was a silent period (no muscle activity) between the low level base contraction and the initiation of the ballistic contraction, the ROFD mirrored that starting from rest. This silent period is indicative of a more neurally coordinated movement. For the Olympic lifters in the crowd, don’t let this research scare you, assuming that this isn’t your first time performing the deadlift.

There is nothing ballistic about a max effort deadlift. In fact, the beginning of the movement is briefly isometric before the bar moves, meaning that ballistic contraction research won’t be as relevant as isometric research. Luckily, there’s some of that, too. A study by Aagaard and colleagues (8) assessed maximal voluntary contraction (MVC) force, ROFD, and EMG activity following 14 weeks of heavy resistance training. The authors reported a significant increase in MVC accompanied by an increase in EMG activity and an increase in ROFD. So, not only does heavy lifting make you stronger, smarter, and more appealing to the opposite sex, it also improves your ROFD due to an increase in neural drive.

Lastly, another study reported no significant differences in torque increases between a ballistic and progressive isometric protocol (9). Essentially, this experiment involved setting the knee extensors at a given angle and either having the subject ramp up to a maximal effort or produce rapid, short duration (e.g. one second) contractions. However, while the difference between the progressive and ballistic protocols was not statistically significant, the ballistic protocol resulted in about a 3 percent greater increase in eccentric torque contraction compared to the progressive protocol and similar changes in slow and fast concentric contractions. Furthermore, the progressive protocol resulted in a 15.7 percent increase in MVC whereas the ballistic protocol resulted in a 27.4 percent increase! Forget statistics! I’ll take the 3 percent.

The problem with much of this research is that it involves measuring activity in an isolated group of muscles, such as the ankle dorsiflexors or the knee extensors, during single joint movements. This is necessary for research purposes because it is impractical to take these measurements during most multi joint movements and in a large number of muscles. Researchers tend to try to isolate one movement and measure the activity of the muscles that produce it. It’s easier to experimentally control an isometric knee extension than it is an isometric back squat. This is good for them but not so good for us because our application of the findings of this research is somewhat limited.

My hope is that most people are more interested in improving their max effort deadlift than their max effort hamstring curl. Despite the single joint nature of the research, we can use what we learned about the neuromuscular system from these studies to improve our training methods.

In order to maximize ROFD, it is best to include both ballistic dynamic movements and ballistic isometric contractions. Ballistic dynamic movements are pretty straight forward. Throw on 35–45 percent of your one rep max (RM) and move the weight as fast as possible for 4–6 sets of 4–6 reps. This seems like a generic recommendation, but it is effective, which is all that matters.

Due to the torque-angle relationships of various joints, certain areas of the range-of-motion are easier (usually toward lock out) than others. To maximize muscular effort, try adding chains or bands to your squats, deadlifts, and bench press movements. For those of you who aren’t familiar, adding chains to the bar increases the amount of force needed toward the end of these lifts. The closer the bar is to the ground (typically the most difficult portion of the lift due to the force-length and force-velocity relationships of the involved musculature), the more the chain will be resting on the floor, resulting in an unloading of the bar. As the bar is raised off the ground, more of the chain comes off the ground, resulting in an increased loading of the bar. Bands work in a similar fashion. The more the band is stretched, the greater the resistance. Bands feel a bit different though because they actively pull you back down. Both of these implements are great tools for improving your ROFD.

Isometric work can be a bit trickier because, in general, improvements from this type of training are joint angle specific (±15º). While it is easy to view this as a limitation of isometric training, it can be a good thing, as there is generally a part of the range-of-motion that is most difficult. Performing the isometrics in that range will allow you to strengthen your weakest areas.

Set yourself up in a squat rack with safety bars set immediately above and below the range that you want to work with the bar in between them. Essentially, you’re just going to push (squat and bench press) or pull (deadlift) against the top safety bar as hard as you can for 3–5 sets of six reps of 1–2 seconds, relaxing 5–10 seconds between each rep. Because you’re pushing against an immovable object, it isn’t necessary to load the bar, although some people may feel more comfortable with some weight on the bar (preferably not much more than 50 percent). The focus should be on short duration, maximal effort contractions. The rest between each rep should allow you to maintain a high performance level on each rep.

An alternative approach is to hold each isometric for a longer duration, such as 10–30 seconds. While I think this type of training definitely has merit, it is extremely fatiguing. The short duration, high intensity, isometric contractions can be performed prior to a training session to help improve neural drive without fatigue hampering the rest of the workout. The longer duration isometrics would probably be best at the end of the session.

Improving ROFD will have a positive effect on the performance of athletes and lifters alike. Research has taken some of the guess work out of applying these strategies. Adding some ballistic movements and isometric contractions into your program may be just what you need to break through a plateau.          

References

1. Desmedt JE and Godaux E (1977) Ballistic Contractions in Man: Characteristic Recruitment Pattern of Single Motor Units of the Tibialis Anterior Muscle. Journal of Physiology 264:673–93.
2. Cavagna G, Dusman B, Margaria R (1968) Positive Work Done by a Previously Stretched Muscle. Journal of Applied Physiology 24:21–32.
3. Edman K, Elzinga G, Noble M (1978) Enhancement of Mechanical Performance by Stretch during Tetanic Contractions of Vertebrate Skeletal Muscle Fibers. Journal of Physiology 281:139–55.
4. Chapman A, Caldwell G, Selbie W (1985) Mechanical Output Following Muscle Stretch in Forearm Supination Against Inertial Loads. Journal of Applied Physiology 59:78–86.
5. van Ingen Shenau G, Bobbert M, de Haan A (1997) Does Elastic Energy Enhance Work and Efficiency in the Stretch-Shortening Cycle? Journal of Applied Biomechanics 13:389–415.
6. Desmedt JE, Godaux E (1978) Ballistic Contractions in Fast or Slow Human Muscles: Discharge Patterns of Single Motor Units. Journal of Physiology 285:185–96.
7. Van Cutsem M, Duchateau (2005) Preceding Muscle Activity Influences Motor Unit Discharge and Rate of Torque Development during Ballistic Contractions in Humans. Journal of Physiology 562:635–44.
8. Aagaard P, Simonsen E, Anderson J, et al. (2002) Increased rate of force development and neural drive of human skeletal muscle following resistance exercise. Journal of Applied Physiology 93:1318–26.
9. Maffiuletti N, Martin A (2001) Progressive versus rapid rate of contraction during 7 wk of isometric resistive training. Medicine and Science in Sports and Exercise 22:1220–27.

Kevin Neeld, CSCS, has helped athletes of all ages fulfill their athletic potential. Through the application of functional anatomy, biomechanics, and neural control, Kevin specializes in guiding athletes to optimal health and performance. He can be reached by email at kn@prodigyperformancetraining.com or through his website at www.KevinNeeld.com.

 

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