The force-velocity relationship states that more muscle force can occur at slower speeds while a muscle shortens. This shortening occurs when you lift a weight. The possible force increases until the slowest movement.
Contracting with no movement will create even more force than lifting at any speed.
Faster movement while lowering allows for even more force than lifting or holding but this quickly plateaus. Therefore the force appears about the same at all speeds during the eccentric. This always allows for more tension than possible for either concentric (lifting) or isometric (holding) contractions at any speed.
A fast speed while lifting causes the thick (myosin) and thin (actin) filaments within a muscle fiber to slide past one another. These filaments create links that form cross-bridges to create tension. Since strength depends upon the average number of links formed, more speed for the same effort will always reduce the tension.
The force described in this relationship comes from tension, the main stimulus for more muscle size and strength. The squeeze you feel when a muscle tenses up to lift, hold, or lower a weight comes from it. Tension also changes with muscle length. Clearly then, understanding how to create enough tension is important for strength training. This interplay of tension and speed in the force-velocity relationship leads to some interesting facts.
- It shows the importance of lowering weights.
Negative work develops the most tension. This seems to occur since the cross-bridges stay together more easily while lowering versus lifting weights. Without some negative training, you will greatly slow strength gains. It seems though that you lower enough with normal reps done to positive failure.
- It explains why fast motions build less muscle than lifting.
Sprinting involves the fast-twitch muscle fibers most responsible for growth. These fibers activate with either fast or heavy muscle actions. Sprinting could never approach lifting heavy though for building size and strength since it occurs too rapidly.
Since sprinting and strength both rely on muscle force, it makes sense that lifting will improve power to a degree beyond what sprinting alone would reach.
You still need to sprint though to develop qualities related to muscular power, and it remains an excellent form of cardio.
- It shows why cardio and strength oppose each other.
Cardio relies on lots of muscle creating lots of movement to raise your heart rate. Strength relies on a group of muscles moving heavier weights slowly to develop tension. Cardio develops best through lifting, and strength develops best through lowering.
- It does not justify different forms of strength and speed.
The force-velocity relationship is a curve. Strength, power, and speed all come from the same force created mostly by fast-twitch fibers. Although speed relies upon some other skills that require specific training, improving one will always increase the potential for the other.
Jumping relies upon elastic energy stored and released in the muscles more so than lifting. The best way to improve your jump potential though would be to train all the lower body muscles heavily. Jumping by nature uses these muscles less efficiently than lifting.
Many powerlifters perform sets with lighter weights explosively. This aims to make them more powerful with heavy weights, but the practice makes little sense. If you were to remove a heavy weight suddenly, you would move fast. Powerlifters simply need to push against heavy weights as fast as possible when things feel tough. Fast movements carry no unique value for them.
- It would seem to justify slow speeds.
If you move too slow though, you fail to recruit the fast-twitch muscle fibers because you apply less effort. Yet we know we need to move slow to generate the most tension. The answer is rather simple though.
You must move as fast as possible when the reps grow difficult. This creates tension in the fast-twitch muscle fibers that spur growth, even if you actually move slowly (which is good). The intention matters more than the actual speed.
This means you probably do not have to move as fast as possible early in the set. Nonetheless, you want to gain the benefits of a pre-stretch. This seems to require you to stay in control yet move as fast as possible while doing so.
- You must increase the load.
If you focus too much on adding more reps, you will come to move too fast before you fail.
The length of the fatigue required to eventually move slow yet strain as hard as possible would take so long as to rely upon the later stage of anaerobic metabolism that produces too much lactic acid or aerobic metabolism that has nothing to do with strength.
Once you establish a reasonable rep range that works for you, say somewhere between 5-15 to start, focus on adding weight. The range of possible reps is rather large and you can likely go as high as 30 or perhaps even more. Nonetheless, this has some limit and you should never need to go higher than 30.
The force-velocity relationship explains why resistance training can improve muscular strength and size so effectively. It also has us conclude that we must lift and lower heavy weights or weights that feel relatively heavy through fatigue in order to have the slower contractions needed to develop the best tension.