First things first
For starters, let’s lay down a few definitions. Within the context of sport science, speed, power, and strength are defined slightly different. Furthermore, for the sake of this article we will discuss iso-kinetic movements, where our joint angles change (a sprint, a bicep curl, etc). We will not be discussing iso-metric exercises where no joint positions change (a plank, a wall sit, etc).
Strength: The ability to generate maximum external force on an object
Speed: Velocity of body motion
Power: Force produced x velocity of the movement
Internal Force: Force produced by one part of the body on another part, this is not considered in the definition of strength.
External Force: Forced produced by the body on an external object
Resistance: External load, drag (such as water in rowing), inertia, friction, gravity, etc
Force Velocity Curve
According to the force velocity curve, it is not possible to exert maximum force and maximum velocity simultaneously. For example, our maximum force is exerted in a 1 rep max deadlift, but the velocity of the lift is relatively slow. On the other hand, we can do an extremely fast snatch or clean with an empty bar though we aren’t creating much force due to the light load. If we want to be stronger and faster simultaneously, we have to shift the force-velocity curve to the right. This means that our maximum force capacity would have to happen at a higher velocity (curve shifts right).
Because peak power happens at around 1/3 maximum velocity, and because power = force * velocity, a right shifted curve allows peak power to increase which means we can tackle harder, jump higher, and lift more faster.
The phenomenon of producing more force more quickly is referred to as Rate of Force Development. Improving RFD is a critical component to living up the the daft punk song. The unfortunate thing here is that the skills of being very fast and very strong are reasonably specific; meaning that powerlifters produce tons of force but they’re not necessarily very fast and that sprinters are very fast but they aren’t going to compete with powerlifters for max strength. Thus, training to improve power (the combo of force and speed) requires that we train both skills in an organized manner as part of our training program otherwise we might wind up super strong but not very fast or pretty fast but only a little bit stronger.
The Physiology of Being a Powerhouse
1) In order to contract, our muscles form cross bridges within a specialized cell called a sarcomere. Contraction happens at a tiny level that accumulates to a big effect because one muscle is made of many many sarcomeres. Though contraction happens pretty quickly, it still takes time.
2) Sliding filaments in the muscle overlap slightly and bond to each other when they receive a nerve impulse, this starts a chemical cascade in the cells. As bonds form between myosin and actin (the thick and thin filaments respectively), they pull the filaments into each-other in a dense overlapping pattern. The more cross bridges that form in the muscle cell, the more force the muscle can produce. You see, each myosin filament has little “heads” that grab onto the actin, after they grab on they produce a cocking action that yanks the actin into the center with force. The more heads that latch on the more force produced and the stronger the contraction.
3) Because high velocity movements happen so fast, less cross bridges form when compared to the quantity that are allowed to form with longer duration high force demanding movements.
4) There are fast twitch fibers (IIX and IIB) and slow twitch fibers (IIA). Fast twitch favor explosive force and strength production but they fatigue relatively quickly, while slow twitch fibers favor endurance and fatigue more slowly. This has to do with differentiation in metabolism and energy use in the cell as well as the motor unit innervating the fibers. Our brain senses what we are trying to accomplish and recruits the fiber types for the job. With only a few exceptions, we recruit type I first and if the task is challenging enough our body recruits more fibers to do the work. This is called Henneman’s Size Principle.
5) The capacity to create force with muscle tissue depends in part on the cross sectional area, i.e. if your bicep is as big as your head it is most likely capable of producing more force than if you’re flexing a string bean. Furthermore, type IIX and IIB muscle tissues tend to have larger cross sectional areas than IIA. Thus, strongmen are bigger around than marathon runners.
6) We tend to improve at movements patterns we train but improving one doesn’t necessarily improve another. Meaning that even if I get really strong at leg press I may not improve my squat or my jump very much even though they look similar.
This is a loose analogy, but picture velcro; if you slide two fuzz and hook layers of velcro on eachother and get them to attach, the attachment will be stronger if more hooks grab the loops than if less hooks grab loops. Muscles are similar, but rather than being pressed onto eachother like velcro, they bond and pull to create a sliding action to create the contraction.
How do we use strength and speed to improve power?
Now that we know the underlying machinery and now that we understand the relationship between force and velocity, we have to understand how that cellular machinery relates to the curve.
When we train we are creating stress to drive adaptation in the body, this stress happens at many levels (neurologic, metabolic, etc). Furthermore, this stress is specific and the adaptation is specific in response. This is called the SAID principle, or specific adaptations to imposed demands.
Because peak power happens at around 1/3 maximum velocity, we are going to focus on strength training as our primary way to improve power and speed work as our secondary way to improve power. Why? Well…
When we train for force production we improve hypertrophy (growth) of the muscle tissue meaning we improve our cross sectional area and our capacity for force production and thus power (remember power = force * velocity). If we are training with heavy weights, a lot of this growth happens in IIX and IIB fibers (the fast ones!), but some occurs in IIA too. This growth is caused by many hormonal, metabolic, enzymatic, etc adaptations but we won’t go into those for now. All we need to know is getting bigger can help us create force and give us more tissue that is capable of moving fast, and once we have that tissue we can train it to move even more quickly in order to improve overall power. Research indicates that speed work alone doesn’t generate as much hypertrophy as we need, but that when used with strength based work it can certainly up our gains so we need to train both.
In part 2 of “So ya wanna be stronger, faster, and move powerful?” we will learn about how to select exercises and plan training in order to maximize power gains.