Heavier Isn’t Always Better: How the Force-Velocity Curve Impacts Your Training

Detric Smith STACK

As coaches, we see the same old story play out in our trainees—the guy who always puts too much weight on the sled, the woman who grabs the heaviest battle ropes, or the person trying to swing a 100-pound kettlebell for time. There’s something in the human brain that tells us “more is always better,” and that extends to weights as well. But how do we explain to our clients/athletes that, just maybe, less is more in some cases?

Thanks to the force-velocity curve, we can help our clients understand that living entirely on one end of the spectrum during our training is rarely a wise idea. Of course, there are exceptions, such as training a strongman competitor or an Olympic sprinter. But for 95% of us, we need a better balance.

What is the Force-Velocity Curve?

In physics, power is the result of force times velocity. Thus, the two form an inverse relationship. According to the Science and Practice of Strength Training, slower velocities allow people more time to form cross bridges within the muscle. Therefore, the muscle can produce more force. This is one reason why a true one-rep max means the bar simply has to move slowly. Obviously, higher velocities means less time for cross bridges and thus, less force. But high velocities are also key to actions like jumping or sprinting.

When depicted on a graph, this inverse relationship between force and velocity forms a curve, as seen below.

Source: Science for Sport

“But…” your clients will ask, “how does this mean you can get better results with less weight? Doesn’t more force mean more muscle?”

Yes, but also no. You can’t forget about total time and training density.

Let’s approach it with an analogy. To generate energy to drive a car or light your house, you need power. The more power you can produce, the more output you get. The same works for the human body. To put it very simply (which your clients will appreciate): the more power you generate, the more muscle tissue you use, and the more calories you burn. The equation for power is force times velocity.

Developing power is extremely important for both athletes and the general population. As we age, power actually recedes at a faster rate than muscle strength. Thus, continuing to train and develop power as we age is a big key to staying functional.

Moving a very light object, such as when throwing a dart, necessitates a short, high-velocity movement. But it doesn’t require much force. You could play for hours and not even break a sweat. Therefore, it doesn’t necessitate much power, either.

On the other hand, lifting an atlas stone requires a massive amount of force, and will definitely be incredibly hard. No matter what you do, that stone won’t move as fast as the dart. This action requires a ton of force, but only slightly more power than our previous example because you’re not multiplying that force by much velocity.

But what about something in between the two, like say, throwing a shot put?

Throwers put their entire body weight and torque in to throwing shot. It’s heavy enough to require significant force, but light enough to move quickly. Thus, it’s quite a powerful movement. With lots of practice applying force at speed, elite throwers can get distance repeatedly. There’s clearly a limit to the amount of throws in one session, but with this equation, they can do more work in more time.

We’d all agree these are different sports, different levels of force and velocity, and different results. So how does that equate to the gym?

What Weights are Right For Me?

First decide if you want to throw darts, lift stones for strongman or throw shot. What type of actions are you looking to enhance in life or sport? Then think back to the force-velocity curve. The F-V curve can be broken into five zones:

  • Max Strength (90-100% 1RM): maximum force, slow movement
  • Strength-Speed (80-90% 1RM): high loads, moved slightly quicker to accelerate power
  • Peak Power (30-80% 1RM): as you can see, this is the largest category. Moderate to medium-high weights moved as quickly as possible
  • Speed-Strength (30-60% 1RM): the opposite of strength-speed. Less weight, geared toward developing velocity under load rather than outright power
  • Max Speed (<30% 1RM): low or no loads, obviously as fast as possible, best for training speed (duh)

If you don’t know your one-rep max, you can use this tool to help you determine which weights fall in which zones for you. You simply have to know how many reps it takes at a certain weight for you to reach failure (the point in a set where you can no longer do another rep). A big problem in the general population is that people will either consistently choose weights that are too heavy or too light for their goals, leading to a failure point that’s too early or too late.

Athletes should follow a well-designed program that considers their specific goals and the specific demands of their sport. For most athletes, this will likely include a mixture of work in several different force-velocity zones, and different cycles of their training may focus on different zones (one period might be spent building max strength while another is spent training max power, for example).

What about for everyone else?

Well, if you want to be really good at a technical sport like throwing darts, then it makes sense to choose the darts version of weight in the gym (which would be 30% of your one-rep max or lower). Lighter weights that allow for incredibly accurate neuromuscular patterns. Something that can be done over and over again without much fatigue to train the skill.

And yes, you can still get results by implementing this type of training. You likely won’t lose weight or build muscle mass if you ONLY use really light weights, but you can improve technique and maximize endurance.

And if you want to be able to lift really heavy weight, you need to train for max strength. Once your technique is solidified, there’s little max strength to be gained by lifting significantly less than your one-rep max. Really, you want to spend most of your time at 90% of your one-rep max and above. Building max strength can be done with heavily loaded Atlas stones, Deadlifts, Squats, Bench Press, etc. Choose a weight that feels incredibly strenuous to do for 1-3 reps (with proper programming and reloads) if you really only want to increase max strength.

But for those of us who have goals like weight loss, building lean muscle mass, metabolic conditioning, looking and moving more athletically, etc., we should gravitate more toward the “shot put” version of the analogy. If you’re not on the extreme ends of the spectrum, moderate weight moved fast (with good technique) is going to get you the best results. You’ll recruit the most motor units and generate the most power, resulting in maximum energy output. Plus, it’s something you can repeat over and over again with moderate rest.

Training for weight loss, longevity and most group training fits this bill. By explaining the idea of the force-velocity curve to your clients, they might pick the moderate weight next time instead of the superbly heavy one and get a few more reps in a 30-second interval. Training density increases, and results follow.

Small, incremental increases in power and production consistently will yield more results than forcing the most weight in one session, every time. Get to know your clientele before blindly programming weights, sets, reps or intervals. While giving them ownership on their workouts increases buy-in, sometimes it’s important to step in. If you see a client consistently biting off more than they can chew, refer to this article to help explain why less is often more.

Photo Credit: skynesher/iStock