Fast Reps Vs Slow Reps: How Quickly Should You Be Moving?

If you’re following Sweat or any of the trainers on social media, you may have seen workout videos and wondered - what’s the difference between fast reps vs slow reps? What speed should I be moving during my workouts? 

The speed at which you perform each repetition in your workout, aka your tempo, is an element of your training you can modify to change how your workout feels and influence your results. 

Different tempos each have their own benefits, so choosing what works best for you will depend on your experience, fitness level, personal goals, and training style. 

Before we get into learning about when you might want to slow things down or speed it up, it can help to understand the difference between the three phases of a strength training exercise, as you may want to focus on control in one phase and power in another.

Eccentric, concentric and isometric - what do they mean?

These three words refer to the different parts of a movement and what happens to your muscle in each phase.

During the eccentric phase, your muscle lengthens, uses less force and the resistance of the load becomes greater than the resistance of your muscles - whether that load be your bodyweight, free weights or gym machines. It can help to think of this as the lowering phase. Examples include lowering into a squat position, the lowering section of a pull-up, or the lowering of your arm in a bicep curl.

The isometric phase refers to the part of the exercise where no motion occurs. This could be a pause at the top of a pull-up or a pause at the bottom of a push-up or squat. If you hear the phrase “isometric hold” or “isometric pulse”, this means holding this position or performing small pulsing movements, which are common in Pilates workouts. 

During the concentric phase, your muscle tension increases and the muscle fibres shorten or contract as you produce force against a load. This tends to be the section of the exercise where you exert power. This could be the part of a pull-up where you pull yourself up towards the bar, the upward part of a push-up, or the part of a squat where you stand up.

During your workout, you can change the pace of each of these phases depending on what you’re trying to achieve.

When are slow reps better?

One of the main scenarios where slow reps can be beneficial is if you are a beginner - either to a specific exercise, a new training style, or if you’re just starting out on your fitness journey. 

Performing each rep at a slower, more controlled pace can allow you to focus on getting your form right, engaging the correct muscles and avoiding using momentum before you think about increasing the speed or lifting additional weights. You also might want to slow the pace down if you’re recovering from an injury or are gradually returning to exercise after having a baby. 

Another time when slowing your reps can be helpful is when you have specific goals to increase your muscle size - aka hypertrophy - which is a key part of Kelsey Wells’ PWR programs on the Sweat app.

With hypertrophy workouts, the focus is on spending more time under tension to boost endurance and growth by fatiguing your muscles. This tends to mean performing a higher number of repetitions and slowing down the eccentric lowering part of the movement, aka feeling the burn.

You can also pause for a second in the middle of the rep (that’s that isometric phase we were talking about!) to challenge your muscles and ensure you’re not using momentum or bouncing motions to move through each rep.

How slow is slow?

When we say slow reps, we don’t mean taking 30 seconds to lower into a squat. We don’t have all day! Generally, we’re talking about a tempo of 2-5 seconds for the eccentric lowering movement to keep your muscles under tension for that little bit longer, and then a faster speed for the concentric phase. 

A research review from 2015 found that a fairly wide range of rep durations (1-8 seconds) can be used to maximise muscle growth, but training at very slow speeds (longer than 10 seconds per rep) can actually reduce the effectiveness of the exercise and is not the best way to achieve hypertrophy or muscle growth.

Another study investigating the impact of velocity of movement on performance came to the same conclusion, stating that very slow velocity may not elicit appropriate levels of force, power or volume to optimise strength and athletic performance.

When getting your tempo right when strength training for muscle growth, it can help to ask yourself - am I performing each rep with control rather than momentum? Am I feeling my muscles engaging?

When are fast reps better?

If you’re wanting to increase your muscular strength and power to lift heavier weights, or you’re trying to get through a very high number of reps, speed can play to your advantage.

For people who love HIIT training like in Kayla Itsines’ programs, you’ll be moving through your reps quickly and powerfully to build your fitness fast. Think sky-high tuck jumps, explosive burpees and speedy mountain climbers. If you’re ever performing over 15 reps or something like Kayla’s 1000-rep challenge, you’d also want to move quickly before your muscles fatigue (unless you really want an extra challenge!).

Likewise, if you’re wanting to make strength gains with your lifting, focusing on speed during the concentric phase of the exercise can get you there - as long as you’ve nailed your technique first. The exercises in Cass Olholm’s programs are great examples of this - you’ll want to focus on speed and power to see strength gains in movements like cleans and snatches. 

A good way to think about this is to imagine you were performing your 1RM (one rep max) for your bench press. If the weight on your barbell is so heavy that you could only perform one rep, performing your rep slowly to spend more time under tension wouldn’t be your focus (or even possible). This is where you focus on power to lift the weight and challenge your strength.

One study from the University of Sydney investigated the effect of contraction speed and the number of sets on strength, finding that training at fast speeds resulted in 11% greater gains than training at slow speeds, which they say is consistent with existing research. 

Another randomised controlled trial comparing traditional resistance training to super slow resistance training found that only the traditional resistance training group reached statistical significance for the strength improvements.

How fast is fast?

This really depends on the specific exercise and training style, but generally, we’re talking one to two seconds per rep. If you were in the middle of a HIIT workout and doing 30 mountain climbers, you might be able to smash out more than one rep per second, while if you were doing walking lunges or dumbbell squats, you might need a bit longer. 

Focusing on speed can be an amazing way to train and build your strength and power - but always make sure your form is correct. Rushing through movements can reduce their effectiveness and increase your risk of injury, so if you need to slow down to do an exercise properly, slow down.

Find your power

When it comes to the slow reps vs fast reps debate, here at Sweat we love a combination of the two to ensure you holistically develop your strength and fitness. Ticking all the boxes for endurance, muscle growth, strength, speed and power sounds pretty good to us!

But we also appreciate that every woman will have different fitness goals and experiences that will lend themselves to certain training styles and tempos - hence the many different program options. Think about what it is you want to get out of your training, then work backwards from there!