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Exercise Repetition Speed During Strength Training

Exercise Repetition Speed During Strength Training

Table of Contents

By Wayne L. Westcott

Exercise Repetition Speed in Strength Training is Controversial

Exercise repetition speed has long been a controversial area in the field of strength training. Although fast movement speeds may permit heavier weight loads, this is largely due to momentum.

For example, if Jim performs barbell curls with his back against the wall he can use an 80-pound weight load. However, if Jim initiates each barbell curl by bending at the waist and rapidly driving his torso upwards, he can lift a 120-pound weight load.

Has Jim enhanced the training stimulus on his biceps muscles by performing fast, momentum-assisted repetitions?  Probably not.  To overcome the inertia of the 120-pound barbell, Jim incorporates the larger muscles of his hips and lower back. 

Although Jim’s biceps assist in this powerful initial movement, once the barbell is in motion they basically go along for the ride.  Momentum-assisted lifts involve large acceleration forces at the beginning and large deceleration forces at the end of each repetition, but relatively low force during the middle range of movement.

So, if we take momentum into consideration, it is easy to see why fast exercise repetition speeds may not be the most effective for targeting a specific muscle. In addition, fast exercise repitition speeds are likely less safe than slower exercise repetition speeds as we will explore next.

Slower Exercise Repetition Speeds are Safest and as Effective as Faster

Jim’s slower paced set of barbell curls with 80 pounds places more consistent stress on his biceps muscles throughout the exercise movement.  This increases the total muscle tension required of biceps and decreases the injury risk to the biceps and joint attachments.  It is therefore advisable for Jim to perform strict repetitions with the moderate weight load to safely and effectively stress his biceps muscles.

Other examples of momentum-assisted movements that are not recommended include bouncing the barbell off the chest during bench presses and bouncing in the bottom position of barbell squats.  Although these rebound actions allow the use of heavier weight loads, they increase the injury potential and should not be practiced.

This information is important for all age groups, but especially useful for senior fitness training.

Research Study One Looking at Exercise Repetition Speed

Is there an ideal exercise repetition speed?  To gain a better understanding of exercise repetition speed and strength development, we studied 163 men and women at three different movement speeds. 

As presented in Table 1, Group A trained at 4 seconds per repetition (2 seconds lifting and 2 seconds lowering).  Group B trained at 6 seconds per repetition (2 seconds lifting and 4 seconds lowering). Group C trained at 8 seconds per repetition (4 seconds lifting and 4 seconds lowering).

Concentric (lifting) Action Equal to or Shorter than the Eccentric (lowering) Action

All of the research participants trained in a private facility with careful instruction and close supervision.  They averaged 10 repetitions per set for 13 different weight stack machine exercises

A trainer providing close supervision of exercise repetition speed

The subjects trained 3 days per week for 8 weeks, with strength assessments taken at the end of the second and eighth weeks.  Overall strength was determined by calculating the average 10-repetition maximum weight load for the 13 different training exercises.

As shown in Table 1, all three training groups made statistically significant and similar improvements (22-23 pounds) in overall strength.  Based on these findings, it would appear that 4-second, 6-second, and 8-second exercise repetition speeds performed on weight stack machines are equally effective for improving muscle strength.

Exercise Repetition Speed Study Specifics

It is noted that Group A subjects completed each exercise set in about 40 seconds (4 seconds x 10 repetitions), Group B subjects completed each exercise set in about 60 second (6 seconds x 10 repetitions), and Group C subjects completed each exercise set in about 80 seconds (8 seconds x 10 repetitions).  That is, all three groups worked their muscles to fatigue within the anaerobic energy system (generally considered less than 90 seconds).

It is also noted that all three groups used moderate to slow training speeds.  That is, the lifting and lowering movements ranged from a moderate movement speed of 60 degrees per second to a relatively slow speed of 30 degrees per second for most of the exercises.

Table 1. Eight-week Changes in Muscle Strength at Different Exercise Speeds (N=163)

Training Protocol

 

(8 weeks)

Reps

 

Per Set

Time

 

Per Set

Mean Weight Load Increase 13 Weight Stack Machines
A.  4 secs/rep 10 reps 40 secs +22 lbs.*
B.  6 secs/rep 10 reps 60 secs +22 lbs.*
C.  8 secs/rep 10 reps 80 secs +23 lbs.*

*Statistically significant improvement (p<.01)

Research Study Two Looking at Exercise Repetition Speed

In this study, 54 participants were randomly assigned to one of two training protocols, both of which performed 10 repetition sets at 6 seconds per repetition.  Half of the subjects trained with concentric muscle actions shorter than eccentric muscle actions (2 sec up, 4 sec down), and half trained with concentric muscle actions longer than eccentric muscle actions (4 sec up, 2 sec down). 

That is, the first group spent about 33 percent of each repetition in concentric muscle action, whereas the second group spent approximately 66 percent of each repetition in concentric muscle action.

Longer Concentric than Eccentric Exercise Repetition Speed

While there were differences in the overall repetition speed among the three training groups in the first study (4, 6, or 8 seconds per rep), one aspect of each exercise protocol remained the same.  In all of these repetition speeds, the concentric (lifting) action was equal to or shorter than the eccentric (lowering) action (2 secs up, 2 secs down; 2 secs up, 4 secs down; 4 secs up, 4 secs down). 

Because the concentric muscle action produces about 40 percent less muscle force output than the eccentric muscle action, it represents the weaker phase of each repetition.  We therefore decided to examine the effects of longer concentric than eccentric muscle actions on strength development.

Exercise Repetition Speed Study Specifics

All of the study participants were assessed on an independent measure of isometric muscle strength before and after the 10-week training program (MicroFit System).  Subjects who spent 33 percent of each exercise set performing concentric muscle actions experienced a 9-pound strength increase. Whereas subjects who spent 66 percent of each exercise set in concentric muscle actions experienced a 12-pound strength increase.

The greater strength improvement (p<0.06) attained by the concentric emphasis group suggests that using a larger percentage of each repetition for the concentric muscle action may enhance the strength building stimulus.  The reason for this may be that more time is spent in the more challenging phase of each repetition, and less time is spent in the less challenging phase of each repetition.

Summary From Our Exercise Repetition Speed Studies

Although fast movement speeds may permit heavier weight loads, Momentum-assisted lifts involve large acceleration forces at the beginning and large deceleration forces at the end of each repetition, but relatively low force during the middle range of movement.

Study One

The first study showed that 4-second, 6-second, and 8-second repetitions are equally effective for improving muscle strength. moderate to slow training speeds

Study Two

The second study showed strength improvement attained by the concentric emphasis group and suggests that using a larger percentage of each repetition for the concentric muscle action may enhance the strength building stimulus.

It may be worth considering an occasional reversal of the standard 2 seconds up and 4 seconds down repetition protocol, at least as an alternative strategy in your strength training toolbox.  If clients are experiencing a strength plateau with the traditional training method, have them try a few weeks with 4 second lifting movements and 2 second lowering movements. Doing this may enhance the training stimulus and elicit further strength gains.

Learn More About Exercise Programming for Special Populations

The American Academy of Health and Fitness is here to help you with this all-important training you will need to be a safe and effective trainer for all age groups. We offer a varied selection of in-depth, advanced continuing education courses.

You will find training in areas such as senior health and fitness, fitness assessment, senior strength training, back stability, nutrition for special dietary needs, lifestyle wellness coaching and cancer exercise. The home study continuing education course SrFit Mature Fitness is definitely one not to miss as you will learn more from strength training expert Wayne Westcott! Certainly, everything you need to create your niche!

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