In today’s world, it’s common knowledge that strength and power are critical components of athletic performance. Coaches and athletes have found various methods to measure and track progress in these areas. But with recent advancements in technology and decreasing equipment costs, velocity-based training (VBT) has become a realistic option for many. VBT provides real-time feedback on an athlete's performance and allows coaches to tailor training programs to meet their specific needs. One of the key tools used in VBT is the Load-Velocity profile (L-VP).
In our previous blog, we introduced the concept of VBT and its theoretical application for strength coaches. One of the key components of VBT is the L-VP. In this blog, we will dive deeper and explore what the L-V profile is, how it is created/measured, how it varies between athletes, how to interpret it, and what its limitations are.
What is the Load-Velocity Profile
I have often heard the terms Force-Velocity (F-V) and Load-Velocity (L-V) used interchangeably, and this isn’t correct. While we often think of force and load in their interaction during resistance training, the two profiles are not representative of the same relationship to velocity...
The concept of a F-V profile is built around the understanding that there is an inverse relationship between the force applied to a resistance and the resulting velocity of muscular contraction. We know that during maximal voluntary contraction, the greater the velocity of a contraction (due to the relatively low resistance) the less force our muscle can produce. The greater the resistance (and slower velocity) allows for more time to produce greater force. Thus, the inverse relationship.
Well, the L-VP is less about individual muscular contraction, and more about systemic expression of force during a movement and the resulting momentum of the system mass. Like F-V, L-V also has an inverse relationship. Assuming the athlete gives maximal effort/intensity, the impulse-momentum relationship tells us that the resulting velocity of the movement will decrease relative to the mass (load) of the system.
Both the F-V and L-V relationships are looked at as profiles because the actual values of the relationships can differ from person to person. We know we will always see an increment/decrement relative to the corresponding points on the scale, but we don’t know where the poles of the scale where being and end. Evaluating where an athlete is positioned on that scale allows us to differentiate between them and their physical characteristics.
The L-V profile is a graphical representation of an athlete's performance at different loads (or intensities). It’s often used in VBT practices to determine an athlete's estimated one rep max (Est 1RM), theoretical peak velocity (V0), theoretical peak force (F0), maximum power output (Pmax), velocity at maximum power, and the load that elicits maximum power output.
The L-V profile is essentially a plot of an athlete's velocity against varying loads lifted. It's created by measuring the velocity of the bar as the athlete lifts a given load. By plotting these data points on a graph, we can identify the athlete's maximum velocity and maximum power output, as well as the load at which they can generate maximum power. In addition, we can use a simple linear regression model to calculate the other outputs.
How is the L-V Profile created?
To create the L-V profile, coaches or sports scientists measure an athlete's barbell (or center of mass) velocity as they lift different loads. This can be done using various tools, including linear position transducers, optical motion capture systems, or wearable sensors.
One popular method is to use linear position transducers (LPTs) that attaches to the barbell. LPTs measure the displacement of the barbell during a lift, which can then be used to calculate velocity. Another method is to use an optical motion capture system that tracks the position of the barbell using advanced cameras (some recent phone apps have shown great promise in matching reliability of more advanced camera systems). Wearable sensors, such as accelerometers and gyroscopes, can also be used to measure barbell velocity by measuring changes in acceleration of the mass.
There are optimal protocols to creating a L-V profile. The most common approach, and often the most valid, is to follow the steps of a one rep max test. This can be very beneficial, especially when creating an initial L-V profile. This is also most familiar with most strength coaches.
Another method is to use at least 5 arbitrary loads. Either estimating a dispersion range for the athlete or using loads relative to their body weight. The former can be of benefit to the coach down the line, for chronological comparison and for ease of set up when testing in a team environment.
For example, to conduct a L-V profile for the Back Squat, the following steps can be taken:
Warm-up: Begin by warming up with a few sets of light squats to get the body prepared for the exercise.
Select the starting load: Choose a starting load that is around 50% of the individual’s estimated one-rep max (1RM).
Perform the exercise: Complete a set of Back Squats with the selected load. Record the velocity of the bar and the power output of the repetition using a velocity measuring device, such as a linear position transducer or a velocity-based training device.
Increase the load: Increase the load by 5-10% and repeat the exercise. Record the velocity and power again.
Continue to increase the load: Repeat step 4 until the individual reaches a load that causes them to slow down significantly or reach a point where they cannot complete a repetition with good form.
** A minimum of 4 different loads is ideal.
Example:
Let’s say an individual’s 1RM for the Back Squat is 200 kg. They would start with a load of 100 kg and complete a set of 5 repetitions, recording the velocity of the bar at the bottom of the squat. They would then increase the load by 10 kg and repeat the exercise until they reach a load of 180 kg. The recorded velocities and corresponding loads would be plotted on a graph to create the L-V profile.
How does the L-V Profile vary between athletes?
The L-V profile can vary widely between athletes, depending on factors such as their training history, muscle fiber type, and neuromuscular efficiency. For example, athletes who have a higher proportion of fast-twitch muscle fibers may be able to generate more force and power at higher loads, while athletes with a greater proportion of slow-twitch muscle fibers may perform better at lower loads.
Additionally, an athlete's fatigue resistance can also affect their L-V profile. Fatigue can cause a decrease in barbell velocity at a given load, which can shift the athlete's L-V profile downward. This can have important implications for training, as coaches may need to adjust an athlete's training load or volume to account for their fatigue resistance.
Interpreting the Load-Velocity Profile
Outside of competitive weightlifting, the primary goal of our training is to improve performance qualities that can’t be quantified by the load on the bar alone. The L-V profile provides valuable insights into an athlete's strength, power, and fatigue resistance. Coaches can use this information to design training programs that are tailored to the athlete's specific needs, with the goal of optimizing their performance.
Load-Velocity at A Glance
One important metric provided by the L-V profile is an athlete's maximum power output. This is the point on the load-velocity curve where the athlete generates the most power. The load at this point is known as the athlete's optimal load. By training at or near this optimal load, athletes can improve their power output and performance.
Another important metric is an athlete's velocity at maximum power. This provides valuable information on an athlete's strength and power capabilities. By tracking changes in an athlete's velocity at maximum power over time, coaches can assess their progress and adjust their training program, as necessary.
In addition to assessing an athlete's strength and power, the L-V profile can also provide insights into their fatigue resistance. As an athlete continues to perform reps at a given load, their velocity will decrease due to the onset of fatigue. The point at which the athlete's velocity drops below a certain threshold can be used to estimate their fatigue resistance.
Looking Under the Hood
Overall, the L-V profile is a valuable tool for assessing an athlete's strength, power, and fatigue resistance. By tracking an athlete's progress over time and adjusting their training program as necessary, coaches can help athletes optimize their performance and reach their full potential. But to truly take advantage of the L-V profile and maximize the data, a coach will need to be a bit more nuanced in their interpretation. Here are a couple of other important key pieces you may want to evaluate.
Linear Regression
While creating the L-V profile is as simple as tracking the velocity at each load, a crucial step is to plot the linear regression line of the data points. This is a necessary step in untapping the full potential of an L-V profile. The regression line is used to calculate some of the most important outputs such as Est 1RM, P0 and F0. It is important to note that the R-squared value of the regression line should be observed to ensure the profile was created with high reliability. If a regression line has a R-squared value less than 0.8, I would evaluate the data more closely and consider reassessing that athlete.
Slope
An important starting place when assessing the L-V profile is the slope of the linear regression line. With use of VBT, there is the implied understanding that there is a linear relationship between velocity and the load applied. Although this relationship is linear, it is not inherently balanced. Meaning both velocity and load are scalar measures in this case. This is what makes L-V profiles so meaningful. We can see the shape of the regression change with the different velocities reached for each athlete, and this can give us an idea of the athletes “power bias.”
The power bias is indicated by which portion of the profile the athlete reaches peak power. Some athletes may be velocity-biased and reach peak power at lighter loads. While some athletes may be force-biased and hit peak power at heavier loads. This can indicate a performance deficit and help the coach identify what training stimuli would be most beneficial for each athlete individually.
Area Under Curve (AUC)
Along with the slope, the area under the curve can be a great way to assess changes in an athlete’s profile, or differences between athletes. I like to think of (and often refer to) the AUC as a “Power Factor.” The reason for this is that power can simply be viewed as force * velocity. With reference to the implications of slope mentioned above, we can think of power being a result of F*v (force-bias) or f*V (velocity-bias). With either case, there is a resulting power output. And with an increase of force, velocity, or both, the athlete will have a resulting increase in power. This will then move the regression line upward, outward, or both.
This is where AUC comes in to play. Since neither load nor velocity can have negative values in this case, they have equal poles of 0. Thus, the resulting linear regression line can be extended to it’s y-intercept and x-intercept, making a right triangle on the plot. And when an athlete either force or velocity capacity (or both), there will be an increase in the area of that right triangle. Simply put, the AUC (or Power Factor), is a simple way to calculate incremental increases in the range at which the athlete has gained power throughout their profile instead of just their peak power.
Limitations of the Load-Velocity Profile
While the L-V profile is a valuable tool for assessing an athlete's performance, it is important to recognize its limitations. One limitation is that it provides a snapshot of an athlete's performance at a specific point in time. As such, it may not fully capture an athlete's long-term progress or potential. Additionally, the L-V profile is influenced by a variety of factors, including an athlete's technique, fatigue level, and psychological state. Coaches and sports scientists must take these factors into account when interpreting the L-V profile and designing training programs.
Although coaches can use some outputs like relative peak power to compare across athletes, you should keep in mind that velocity can be a sensitive measure with regards to athlete output. Like all tests and assessments, coaches should consider external factors and that may influence results and account for them accordingly. Collecting multiple profiles over time allows the coach to understand normal variance of each athlete and gain insight into what significant change looks like.
Finally, the L-V profile should not be used in isolation when assessing an athlete's performance. It should be combined with other metrics, such as maximal strength and power output, to provide a more complete picture of an athlete's capabilities.
Conclusion
The L-V profile is a valuable tool for assessing an athlete's strength, power, and fatigue resistance. By measuring an athlete's velocity at different loads, coaches and sports scientists can gain insights into their performance and design training programs that are tailored to their specific needs.
However, it is important to recognize the limitations of the L-V profile and to use it in conjunction with other metrics when assessing an athlete's performance. By taking a holistic approach to athlete assessment and training, coaches and sports scientists can help athletes reach their full potential and achieve their goals.
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