Rate Of Force Development Part 2: Training and Increasing RFD

Last post, I went over some of the terms and definitions of rate of force development (RFD). I also mentioned motor units (MU) and if, at this point, you have no clue what I’m talking about, go back and read it. It’s right here. Why should you care about increasing your rate of force development? Answer: power sports (which is every sport to some degree) are dependent upon the ability to produce high levels of force at any given moment, like running away from a T-Rex.

There are two main ways research and experience backs up to train RFD: explosive strength training (Newton et al. Med. Sciences Sports Exer. 1999) and maximal load training, i.e. picking up heavy stuff. (McBride et al, J. Strength and Conditioning Research 2002). It should be noted that most of the research has been done with isolated muscles/movements (it’s a lot easier to test the quadriceps muscle in a leg extension machine than the various muscle groups in a deadlift) and so it can be a little tricky to apply to real life. However, where science has holes, the experience of coaches fills the gap!

First: force = mass x acceleration Keep this in mind…

Explosive training (speed work) is taking a sub-max load (say, 50% of your one rep max) and moving it as fast as possible, with good form obviously, for 1-3 reps per set. That’s key- as fast as possible. Those high threshold motor units, the ones that produce the most force, are recruited to move that weight quickly by contracting quickly. Even though the load is light, the acceleration is high. By challenging your system to move loads supa fast (actual speed measurement), we can increase the force production by increasing the acceleration part of the equation. This is one way to train and increase RFD, by working on the "speed" (or "velocity" for the nerds) part of the equation.

Typically at SAPT, we program 1-3 reps for 6-8 sets with a strict :45-:60 rest period. Why the rest parameters? We want to keep the nervous system “primed” and if the rest period is too long, we lose a bit of that ability to send rapid signals to the muscles.

Maximal load training, aka picking up some freakin’ heavy weight, will typically be above 90% of your one rep max, likewise we keep the rep range between 1 and 3 (mainly because form can turn to utter poo very quickly under heavy loads if the volume is too high). This untilizes the other part of the force equation, mass. If the acceleration is low, the mass has to be high in order to create a high force production. Once again, neural drive is increased and those high threshold MU’s are activated. The threat of being crushed beneath a heavy bar can do that.

Bottom line: As the an athlete's RFD increases –> the recruitment threshold of the more powerful motor units decreases –> more force is produced sooner in the movement –> heavier weights can be moved/athlete becomes more explosive in sport movements.

Think back on poor lifter B from last post who had a really low RFD during his 400lb deadlift attempt. Being the determined young man that he is, he trained intelligently to increase if RFD through practicing speed deadlifts (to get the bar off the floor faster) and maximal training, (to challenge the high threshold units to fire). Pretty soon, instead of taking 3 seconds to even get the bar off the floor, it only takes 1 second of effort and instead fo straining for 5 seconds just to get the bar to his knees, he’s able to accelerate through the pull and get it to lock out in just under 4 seconds. Success!

For sake of the blog post, we could assume he always had the capability of producing enough force to pull 400lbs, but could produce it fast enough before his body pooped out. Now, with his new and improved RFD, 400lbs flies up like it’s nothin.’

Another thing to keep in mind is the torque-angle relationship during the movement. Right… what?

All that means is the torque on the joints will change depending on their angles throughout the movement, thus affecting the amount of force the muscles surrounding those joints must produce. For example, typically* the initial pull off the floor in a deadlift will be harder than the last 1-2 inches before locking out due to the angle of the hip and knees (at the bottom, the glutes are in a stretched position which makes contracting a little tougher than at the top when they’re closer to their resting length.) Same concept applies to the bench press, typically** the first 1-2 inches off the chest are more difficult than the last 1-2 inches at lockout. The implication of all this being  the muscles will have different force-production demands (and the capability to meet those demands) throughout the exercise.

Knowing this, we can train through the “easier” angles and still impose a decent stimulus to keep those higher threshold motor units firing the whole time. How?

With chains and bands! Yay!

Aside from looking totally awesome, chains provided added resistance during the “easier” portions of the exercise to encourage (read: compel) muscles to maintain a high force output throughout the movement. Watch Conrad, The Boss, deadlift with chains: 

At the bottom, when the torque-angle relationship is less favorable, the weight is the lightest and as he pulls up, the weight increases as glutes must maintain a high  level of force output to complete the deadlift. No lazy glutes up in hea’! Bands produce a similar effect. Check out the smashingly informative reverse band bench post Steve wrote here.

There are other ways and other aspects to discuss (like the fore-velocity curve... but that is a tale for another day!), but quite frankly, this blog post is reaching saga-like proportions so I’m going to cut it here. And remember kids:

*unless your name is Kelsey Reed and you have a torso 6 inches long… but can’t lock the pull out.

** unless your arms crazy long.