Why Tempo Matters in Strength Training: Maximizing Motor Unit Recruitment and Performance
Understanding the Motor Unit and Why Tempo in Training Matters
If you’re serious about strength training, understanding how your body works beneath the surface is essential for unlocking your true potential. Many athletes, especially in strongman and powerlifting, focus on lifting heavy weights but overlook one of the most critical aspects of training—tempo.
Tempo isn’t just about how fast or slow you lift; it’s about controlling every phase of an exercise to maximize muscle activation, strength gains, and control the adaptation that you’re getting from your training. Yet, many athletes don’t adhere to prescribed tempos. Today, we’re going to explore why tempo matters, how it connects to motor unit recruitment, and how ignoring it can impact your training outcomes.
From the Beginning: The Motor Unit and Muscle Activation
At the core of every movement you perform is the motor unit, which consists of a motor neuron and the muscle fibers it controls. When you lift weights, your brain sends an electrical signal to the motor neurons, which then activate the muscle fibers, causing them to contract and generate force. But it’s not as simple as firing all muscle fibers at once—your body uses an efficient system to activate these units based on the task at hand.
Muscle Fiber Types and How They Impact Your Strength Gains
Muscle fibers are categorized into two main types: Type I (Slow-Twitch) and Type II (Fast-Twitch).
Type I (Slow-Twitch) fibers are used for endurance and low-force tasks, like maintaining posture or performing high-repetition work.
Type II (Fast-Twitch) fibers are recruited for powerful, high-force movements, like lifting heavy weights or sprinting.
If your body recruited all of your motor units like a light switch, you’d be putting your maximum effort into every trivial movement you made in life like brushing your teeth or picking up your keys. Your body can create gentle forces to create subtlety, and precision but to do so it can only recruit a portion of the available motor units.
In order to determine which ones to recruit, your brain utilizes a sequence. It starts by recruiting the smallest motor units first and progresses to the largest as the task demands it. This gives the body the most range when it comes to force production because it allows for very small motor units to be activated alone and create very small amounts of force.
It also starts by recruiting the Slow-Twich fibers first, escalating to the Fast-Twitch fibers as the task demands. This also allows for the body to be very efficient, only expending energy on the more expensive Type II fibers when absolutely necessary.
The question I hope you’re asking your self is, “But how does this tie into tempo?” Let’s explore that further.
How Motor Unit "Twitches" Impact Muscle Control and Strength
For a muscle fiber to contract, the brain has to send a signal to the motor neuron. The fibers in that motor unit will start relaxed, briefly contract and then relax again. This process, where the brain sends the signal and the motor unit activates and deactivates is called a twitch. This where the terms “fast-twitch” and “slow-twitch” fibers come from.
It is essential to understand that this is the fundamental building block action taken when our bodies move. If we need more force than a single motor unit can produce, the brain has to send multiple signals and initiate more twitches. If we need to sustain an effort and create force over time, then the brain has to send a stream of signals to create repeating twitches.
A lot of people imagine muscle contractions to work like a hydraulic system, where as long as there is pressure there is action. I like to use the analogy of someone playing the snare drum. One twitch is one tap of the snare. If you want more sound out of each tap, you need a bigger drum or more drummers to make the sound bigger. If you want a constant sound, you have to keep tapping in rapid succession to maintain it.
Holding a single contraction over time is like a drummer tapping a snare so fast that we can’t hear the break between taps. It just comes out as a single constant hum. This is where tempo becomes so critical. Controlling the speed and duration of each exercise allows us to better control how many motor units are recruited, in what position, at what rate, and for how long.
Intra- and Inter-Muscular Coordination: Maximizing Muscle Efficiency
Intra-muscular coordination refers to how well your body can recruit motor units within a single muscle. The better this coordination, the more efficiently you can generate force from that muscle. If the body needs a lot of force from the muscle quickly, the brain needs to be able to initiate a lot of twitches simultaneously. If the body needs to move something very heavy, then the brain needs to be ready to escalate to the largest and most powerful motor units it has access to. These are tasks that the brain and body can grow to become better at performing through training.
On the other hand, inter-muscular coordination refers to how well multiple muscles work together to perform complex movements. The body has over 600 muscles in it, and they are all under the command of the brain at any given time. Just zooming in on the dip/drive of a push press can show us how complicated this coordination can be. As the bar falls, there is an isometric contraction in the upper body to create a front rack. The quads are relaxing their force production just enough to allow the weight of the bar and body to bend the knees. The glutes are having to read that drop and contract just enough to let the knees drift forward, but not so far that the hips go backward. Your brain is coordinating all of this through the highly detailed and specific dissemination of signal and the creation of the resulting twitches.
When you apply a tempo, you change the nature of the task that the brain has to coordinate. This can help you to highlight specific points in a technique where the athlete struggles and create a productive stress that results in adatation. It can also help you to create specific adaptations in the body with conventional exercises that transfer to more sport specific actions.
Types of Strength: Real Applications for Strongman and Powerlifting
In this section, I want to highlight just how many different types of strength there are that the body can be built to display. You should note that this list wasn’t meant to be exhaustive and that there are probably some missing pieces. As you read through it, do so while referencing back to earlier portions of the blog post. Try to think about the motor recruitment process and how it might behave in different muscles during different exercises as their used in protocols to develop these strengths.
1. Gentle Lifting:
The same body capable of curling a 100lb dumbbell must also be able to precisely control smaller, delicate movements—like lifting an apple to take a bite. This is done by recruiting only a small number of motor units, just enough to accomplish the task. The brain carefully controls the recruitment to ensure fine motor control and minimal force is applied.
2. Absolute Strength:
This refers to the athlete’s ability to lift as much weight as possible for a single repetition, regardless of time. It’s seen in powerlifting, where the athlete pushes their limits in exercises like the squat, bench press, or deadlift. Absolute strength requires the recruitment of the maximum number of motor units to generate peak force, and it taxes the nervous system heavily. The brain commands nearly all available motor units to fire in a coordinated effort, sustaining that output as long as necessary to complete the lift.
3. Explosive Strength:
Explosive strength is the ability to generate maximum force in the shortest time possible, often described as "power." Here, the body must rapidly recruit motor units and progressively engage more muscle fibers in a brief window to generate peak force quickly. The faster the motor unit recruitment process, the more muscle is activated, and the more powerful the movement becomes. This is seen in movements like Olympic lifts or jumps.
4. Starting Strength:
Starting strength is the body’s ability to initiate movement from a static position, like in an Anderson squat or pin press. It requires a large number of motor units to be recruited nearly simultaneously. The brain sends an intense initial signal to overcome inertia, rapidly engaging a significant portion of motor units in the targeted muscles to get the bar or object moving.
5. Reactive Strength:
This strength refers to the body’s ability to transition from an eccentric (lengthening) contraction to a concentric (shortening) contraction, such as in plyometrics or the bottom of a squat. It involves a brief isometric contraction at the moment of reversal, requiring the motor units to re-fire and adjust quickly. Effective reactive strength allows the muscles to store and release elastic energy, maximizing force during the concentric phase.
6. Isometric Strength (Overcoming):
This isometric strength occurs when the athlete applies force to an immovable object, such as pushing against a wall. The brain recruits as many motor units as possible in that specific position, but since the object cannot move, the force cannot result in concentric contraction. This static effort pushes the body to its limit in a fixed position.
7. Isometric Strength (Yielding):
This is when the body resists an external force trying to displace it, such as holding a plank or maintaining a squat position. The brain recruits only enough motor units to hold the position against the external force. If more force is produced, it would result in movement and thus become concentric contraction. Yielding isometric strength is about maintaining a controlled equilibrium.
8. Concentric Strength:
Concentric strength is the ability of a muscle to shorten while overcoming resistance. During a concentric contraction, motor units are recruited sequentially as needed, increasing in number depending on the resistance. For example, lifting a weight off the ground requires motor units to fire in waves, shortening the muscle fibers and moving the object.
9. Eccentric Strength:
Eccentric strength is the ability to control and absorb external forces as a muscle lengthens, such as when lowering a weight. More motor units are recruited as needed to resist the external force, but the contraction type allows for greater force production compared to concentric movements. Eccentric strength is crucial for deceleration and preventing injury.
10. Rate of Force Development (RFD):
RFD refers to how quickly the athlete can recruit motor units and generate force. It’s the speed of motor unit activation, dictating how rapidly the body can transition from relaxed to full engagement. Higher RFD means the athlete can achieve peak force faster, crucial in sports requiring fast, powerful movements like sprinting or throwing.
11. Stabilizing Strength:
Stabilizing strength is the ability to maintain joint and body stability during movement or in static positions. This involves a fine-tuned and continuous recruitment of motor units, primarily in the stabilizing muscles, to counteract any unwanted movement or force.
12. Isometric Strength Endurance:
This is the body’s ability to maintain a static position over time. The brain continuously sends signals to keep motor units firing, but since the muscle fibers don’t get a chance to rest, they fatigue over time, requiring additional motor units to take over as others fail. Eventually, all motor units may be recruited, leading to exhaustion.
13. Strength Endurance:
Strength endurance is the ability to sustain repeated bouts of strength over a period of time. It involves the cyclical recruitment of motor units, where motor units are engaged, rest briefly, and then re-engaged as needed. This cycling allows the muscle to perform strength tasks for longer durations without fatiguing too quickly.
14. Power-Endurance:
Power-endurance is the ability to generate powerful movements repeatedly over a sustained period. It involves recruiting motor units at high speed, with minimal rest between efforts. Athletes in sports like football or rugby need power-endurance to maintain explosive actions over extended periods.
15. Speed-Endurance:
Speed-endurance is the ability to maintain high-speed efforts over time. Here, motor units are recruited for quick, repetitive contractions, with the emphasis on maintaining force output at high velocities. Athletes like sprinters need this to maintain near-maximal speed over the duration of their race.
The Critical Role of Tempo in Maximizing Strength and Muscle Recruitment
We’ve gone over a lot already, so I say it’s high time we actually dive into the topic at hand: Tempo!
In general tempo refers to the rate at which we perform different aspects of an exercise. Alongside the intensity and rest times it is one of the three pieces that I put into exercise instructions for every exercise you’ll find in one of my published training programs.
Generally, i use a 4-digit code to explain the tempo to my athletes. This 4-digit code can be applied to just about any exercise, and is always read in the same order. The code looks like this: X/X/X/X
The first character in the code is always the concentric. This is the portion of a rep where the muscles are contracting. In the squat, this is the portion of the rep where the athlete is coming up out of the hole back to lockout. In a deadlift, it is the lift off the ground. In a pull-up, it is the athlete lifting themselves to the bar. No matter the exercise, this is where the muscles are contracting.
The second character is the hold at the end of the concentric. Sometimes I’ll call this the squeeze, but there are a lot of exercises where the athlete is going to be relaxing in this portion of the exercise. The back squat is the best example. For the back squat, this is the portion of each exercise where you’re standing upright with the bar. In contrast, for exercises like a quad extension, this is the most strenuous portion of the rep.
The third character is the eccentric, or the time it takes on each rep to let the muscles stretch. A lot of times you’ll hear this portion of the rep called the negative, and it is one of the most commonly manipulated elements of an exercise. It is always the opposite of the concentric.
The last character is the hold at the extended portion of the lift. Sometimes I’ll call this the stretch, but again there are a lot of exercises where the athlete si going to be relaxing here. The deadlift is the best example. It is also similar to the squeeze in that it can be the hardest part of an exercise. Holding the bottom of a back squat can be torturous.
Most of the time the tempo code will only have one or two numbers in it. The other characters are just dashes. The dash means that you should be working through that portion of the tempo as fast as you possibly can with appropriate technique. Here are a few code examples and what they might look like for some exercises:
TEMPO: -/-/3/2. For the squat, this would mean that you’re taking 3 seconds to lower the bar into the hole, then holding the bottom for 2 seconds before exploding back up to lockout and starting the next rep as soon as possible afterwards.
TEMPO: 3/-/3/-. This is an example of an oscillating tempo, where the bar is going up and down at the same speed with no break between the concentric and eccentric phases. 3 seconds on the way up then immediately changing direction for 3 seconds on the way down.
TEMPO: -/2/3/-. For a bicep curl, this would mean curling the weight as fast as manageable with good technique, then holding the squeeze at the top for 2 seconds before taking 3 seconds to lower the weight. This would be a great tempo for something like a spider curl where the tension isn’t released at the top of the curl.
It should be noted that there are times where the necessary tempo can’t be communicated with a 4-digit code. I love to prescribe paused deadlifts to athletes, where the athlete has to break the bar off the ground and bring velocity to zero before ramping back up and finishing the lift. The code can’t communicate this so the athlete will need to know where to pause and for how long.
Tempo allows for me as the coach to take a single exercise and an understanding of motor unit recruitment to develop a vast variety of strengths in an athlete. Suddenly we can become strength development snipers, targeting very specific aspects of an athlete’s sports performance to make huge impatcts on their overall performance. The athlete doesn’t just develop overall leg strength… they develop the ability to absorb force in the high squat position and quickly transition into explosive strength that results in a higher vertical jump.
Sometimes the required tempo can’t be described with that code. Things come up like pauses in specific portions of the lift, or multiple reps in a portion of the lift before completing the lift.
How to Accurately Control Tempo for Strength Training: Tips and Tricks
Adding tempos like these can create a lot of stress on the athlete. if it didn’t they probably wouldn’t need a ton of exposure to these tempos in the first place. The acute stress of holding these tempos isn’t fun, and I think that is the reason that they are so often cheated or skipped altogether.
If an athlete is going to see the benefits of the tempo, they need to be held accountable to the tempo. That means either a coach pushing them, or having the self-discipline to make it happen for themselves. If they do have a coach, then the coach can hold the stopwatch and ensure that they’re holding things as long as they’re supposed to.
If there’s no coach, the athlete has to do that job for themselves. It is a tough thing to do, but the better the job that they do the more robust their adaptations will be. Here are some tips to that solo athlete so that they can be most successful.
Never count in your head. When you’re in the bottom of a back squat holding a pause, time goes by slower than when you’re at the microwave waiting for your prepped food to heat up. Your perception of time is going to lead you to count too fast and you’re going to cut your tempo short. I’ll explain more about why this is so costly in a second.
Use a metronome app on your phone. You can find freebies in your app store that will play through your headphones over your music. Set the BPM to 60 and you’ll get a tick every second that goes by. As you perform the movement you’re just counting the ticks that you hear over your headphones.
Set a timer somewhere you can see it in your technique. There are times where I’m playing music through speakers in the gym that everyone can hear so I don’t want to annoy everyone with the clicks. For the deadlift or the squat, I can just set a timer on the floor a few feet out in front of me to let the timer keep up with my timer.
Have someone else in the gym count your tempo for you. It seems crazy to me that you’d be in the gym and not have access to a stopwatch of some kind, but should this weird situation arise you should at least let someone else count in their head. That way at least the person counting is fighting the negative or holding the pause and experiences that time distortion that happens in that stressful situation.
The last tip that I have is to make sure that the count always starts with “0”. If you have a five second negative and you initiate that tempo by saying “1”, then you’re only going to have 4 seconds of time in that tempo. You might be thinking to yourself, “What’s the big deal, it’s only 1 second.” Well here’s the big deal: That’s 20% of your tempo.
If you miss even a second of your prescribed tempo, it means that you’re skipping a material chunk of the work. A set of 5 reps with a -/-/3/2 tempo implies a minimum of 25 seconds of time spent under tension. If you skip one second of the tempo in either the negative or the stretch, then you’re missing out on 5 seconds of the tension. You might as well have just ended your set a rep early.
THis is also why it is so important you never count for yourself. If you turn a 5-second negative into a 3-second negative by counting too fast by accident, the workload ends up being 60% of what it was meant to be. You will not get the benefits of the prescribed tempo if you cut it by that much.
Conclusion
The relationship between the brain and the body is pretty freakin cool. Each motor unit is a cluster of muscle fibers with a governing motor neuron that receives orders directly from the brain. Each muscle is made up of these motor units, allowing for the brain to scale up and down the amount of force that muscle is producing. The brain is regulating this force in over 600 muscles in the body simultaneously to create complex muscle actions. It does so by sending an individual signal to each motor unit, initiating a single contraction/relaxation cycle called a twitch.
Through the use of controlled tempos, we can force the brain and body into precise situations to elicit specific adaptations. The thing is that it only works if you’re truly adherent to the tempo as it’s prescribed. Counting in your head should never be an option because you’ll always short-change the tempo. You need to get a metronome or a stopwatch to ensure that the tempo is happening exactly as its intended. Shorting the tempo even by a second can materially change the stress on the body and reduce the potency of the protocol.