Training frequency is one of the most important variables in training along with intensity, effort character and load volume. It refers to the number of times per week that a particular muscle group (e.g. pec, back, quads…) or movement (e.g. bench press, squat, deadlift, deadlift, military press…) is trained and is largely determined by four factors:

Availability of each person: days per week that can be trained and time available each day.
Load volume of the routine: number of sets per week for a given muscle group or movement.
Specific needs of each target.
Recovery capacity of each person.
The frequency of training is not a new topic, but, like everything else, it requires an update from time to time to remind us of basic concepts that may have been diluted along the way and to refocus us to be able to apply what we know in the most effective way possible. The aim of this article is, precisely, to put us in situation of what we know today and how we can distribute our training routines according to the circumstances of each one.

WHAT IS THE IDEAL FREQUENCY FOR EACH PERSON?
There are four points that dictate the ideal training frequency for each of our objectives:

Total days of training per week (availability of each person).
Optimal range of daily sets per muscle group or per movement.
a. In the case of hypertrophy, the rate of protein synthesis,
b. In the case of absolute maximum strength, the accumulation of residual fatigue.
The daily recovery capacity of each individual.

  1. Total training days per week (availability of each person).
    Obviously this is the point that determines in the first place the ability to put in more or less frequency per week and does not depend on theoretical factors of training optimization.

Optimal range of daily sets per muscle group or per movement.
Training volumes greater than about 10 effective sets per muscle per workout are generally more harmful than helpful when training hard and with quality sets [1,2]. At this point, rather than adding more volume per session, training frequency should be increased to accommodate higher training volumes per week (Figure 1).

3a. Hypertrophy and protein synthesis.
In the case of hypertrophy the third factor to consider in establishing an optimal training frequency is protein synthesis. There are strong benefits to be gained from evaluating research results on acute muscle protein synthesis after training and its long-term effect. Muscle protein synthesis correlates positively with muscle mass gains [3-5].

In a strength training session, the fibers of a muscle experience a mechanical load. This mechanical load is detected by mechanoreceptors, leading to anabolic signaling. This signaling triggers an increase in the rate of muscle protein synthesis within each muscle fiber that has been subjected to that overload. That increase in the internal rate of muscle protein synthesis is what causes a higher protein content within the worked muscle fibers and, in the long run, what largely accounts for the increase in muscle size.

Therefore, the length of time during which the rate of muscle protein synthesis is elevated after a workout is quite important and will largely determine the frequency of training per muscle group per week, and is also different between beginners and advanced (Figure 2).

This behavior of protein synthesis determines in part the frequency with which we must expose ourselves to the training stimulus and, consequently, determines the frequency of training. Among all the research that has addressed in one way or another how muscles of different sizes respond to different training frequencies while maintaining volume, the clear and natural tendency is that there is an inverted U-shaped curve that assumes that training the same muscle group two or three times per week is optimal in terms of the volume-frequency-hypertrophy ratio achieved [1,6]. However, when the volume is not equalized, it is shown that increasing the training frequency allows more effective total volume per week to be included and, consequently, the increase in size is greater (Figure 3)

Therefore, depending on the days trained per week and allocated to each muscle group, an average gain of 0.08% per workout could be expected in the case of low frequency and 0.15% per workout in the case of high frequency. Each additional day of frequency increases weekly hypertrophy by 0.11%. That is, each additional day of frequency leads to 22% more hypertrophy, on average [7].

Although high training frequency might seem to imply greater fatigue during the week, we see that, theoretically and objectively, high frequency is superior in the short, medium and long term to low training frequency. The differences are statistically significant in all time frames (short, medium and long term), but in a practical visual way, significant improvements will be noticed in about 12 weeks.

3b. Absolute maximal strength and residual fatigue accumulation.
Due to the very nature of strength adaptations which, we recall, are different at the systemic and peripheral level, the basis for understanding the optimal training frequency differs with respect to a hypertrophy routine and focuses, above all, on improving motor learning and control, reducing antagonist coactivation, and avoiding residual fatigue as much as possible [8].

Thus, the summary of the current literature dictates that, even when volume and intensity are matched, it appears that higher training frequencies lead to greater strength gains [9-12]. This means that distributing a given number of sets over more training days appears to increase strength gains, especially for upper body push exercises (e.g., bench press).

In most analyses, higher frequencies appear to lead to 20 – 25% faster strength gains in both trained and untrained lifters, and there appears to be a fairly linear increase in unit gains from increased weekly frequency up to 4x frequency, however, we do not have enough studies with frequencies above 4x per week to say that beyond that frequency greater improvements are obtained. Therefore, distributing the weekly sets of a given movement over as many days as possible is better for gaining absolute maximal strength than doing it on fewer days.

The explanations behind these results are mainly two:

Greater acquisition of higher skills and motor learning. In general, skills are learned and mastered faster when practiced more frequently.
Increased frequency improves the average quality of training (little loss of speed intraset and between sets). If you have to do three sets of squats in one session, all three sets will probably be pretty good. If you do it twice more in a week, you will have accumulated nine high-quality sets. However, if you were to do all nine sets in a single training session, the quality of those sets would probably start to decline long before you finish your ninth set.
Spreading the weekly sets of a given movement over as many days as possible is better for gaining absolute maximum strength than doing it on fewer days. Increasing frequency improves the average quality of training.

  1. Recovery capacity of each person.
    Each person’s ability to recover is largely determined by training load management and recovery strategies such as more or less daily physical activity, diet, rest, etc.

RECOMMENDATIONS FOR FINDING THE BEST TRAINING FREQUENCY FOR YOU
If you are currently progressing on a low frequency training program (try not to make it frequency I for all muscle groups, although it might be for some, depending on your circumstances, experiences and goals), don’t change anything. However, when you plateau, consider increasing your training frequency.
Many lifters, anecdotally, find that they can tolerate higher frequencies for some exercises or muscle groups, but not for others. Higher training frequencies are worthwhile, but keep in mind that responses are personal and may not reflect the average response.
If you decide to increase training frequency, start by spreading the current training volume over more days per week.
Example: 15 sets of bench presses per week:
15 sets in 1 session,
7 sets in 1 session + 8 sets in another session,
5 sets in 3 different sessions,
4 sets in 3 different sessions + 3 sets in 1 session.

Do not increase the volume until you see how you respond and recover between sessions. It will probably take 3-5 weeks to get an indication of results.
If training exclusively for hypertrophy at a high frequency, consider alternating between more and less demanding exercises for each muscle group. For example, if you do squats on Monday to emphasize quads or knee dominants; do something lighter like press or Bulgarian squat on Tuesday or Wednesday,
Use main and reminder sessions throughout the week for different movement patterns (knee dominants, hips, thrusts, pulldowns…) and intermingle between them. Remember that the total weekly volume is more important than the extreme, acute fatigue of a single session.
Primarily, higher frequencies should be implemented to highlight weak points, or when the weekly volume for a given muscle group is low. Secondarily, to improve on a particular movement.
Depending on the time available each day, consider doing double sessions on some days of the week. Perhaps you can have two 45-minute times of the day that would be more productive in the medium to long term than squeezing in a single 60-minute session per day and using the rest of the free time for other chores. Remember again, to get results you have to keep your mind cool enough to know what you should do (and not just what you want to do at any given time).
Bibliography and references
Schoenfeld, B. J., Grgic, J., & Krieger, J. (2019). How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency. Journal of sports sciences, 37(11), 1286-1295.
Heaselgrave, S. R., Blacker, J., Smeuninx, B., McKendry, J., & Breen, L. (2019). Dose-response relationship of weekly resistance-training volume and frequency on muscular adaptations in trained men. International journal of sports physiology and performance, 14(3), 360-368.
Brook, M. S., Wilkinson, D. J., Mitchell, W. K., Lund, J. N., Szewczyk, N. J., Greenhaff, P. L., … & Atherton, P. J. (2015). Skeletal muscle hypertrophy adaptations predominate in the early stages of resistance exercise training, matching deuterium oxide-derived measures of muscle protein synthesis and mechanistic target of rapamycin complex 1 signaling. The FASEB Journal, 29(11), 4485-4496.
Hulmi, J. J., Kovanen, V., Selänne, H., Kraemer, W. J., Häkkinen, K., & Mero, A. A. (2009). Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression. Amino acids, 37(2), 297-308.
Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., … & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), 376-384.
Schoenfeld, B. J., Ratamess, N. A., Peterson, M. D., Contreras, B., & Tiryaki-Sonmez, G. (2015). Influence of resistance training frequency on muscular adaptations in well-trained men. The Journal of Strength & Conditioning Research, 29(7), 1821-1829.
Nuckols, G. (2019). Training Frequency for Muscle Growth: What the Data Say. https://www.strongerbyscience.com. Retrieved March 15, 2021 from https://www.strongerbyscience.com/frequency-muscle/.
Badillo, J. J. G., & Serna, J. R. (2002). Bases of strength training programming (Vol. 308). Inde.
Grgic, J., Schoenfeld, B. J., Davies, T. B., Lazinica, B., Krieger, J. W., & Pedisic, Z. (2018). Effect of resistance training frequency on gains in muscular strength: a systematic review and meta-analysis. Sports Medicine, 48(5), 1207-1220.
Gomes, G. K., Franco, C. M., Nunes, P. R. P., & Orsatti, F. L. (2019). High-frequency resistance training is not more effective than low-frequency resistance training in increasing muscle mass and strength in well-trained men. The Journal of Strength & Conditioning Research, 33, S130-S139.
Franco, C. M., Carneiro, M. A., de Sousa, J. F., Gomes, G. K., & Orsatti, F. L. (2019). Influence of High-and Low-Frequency Resistance Training on Lean Body Mass and Muscle Strength Gains in Untrained Men. Journal of strength and conditioning research.
Damas, F., Barcelos, C., Nóbrega, S. R., Ugrinowitsch, C., Lixandrão, M. E., d Santos, L. M., … & Libardi, C. A. (2019). Individual muscle hypertrophy and strength responses to high vs. low resistance training frequencies. The Journal of Strength & Conditioning Research, 33(4), 897-901.

TRAINING FREQUENCY. UPDATE 2021

Training frequency is one of the most important variables in training along with intensity, effort character and load volume. It refers to the number of times per week that a particular muscle group (e.g. pec, back, quads…) or movement (e.g. bench press, squat, deadlift, deadlift, military press…) is trained and is largely determined by four factors:

Availability of each person: days per week that can be trained and time available each day.
Load volume of the routine: number of sets per week for a given muscle group or movement.
Specific needs of each target.
Recovery capacity of each person.
The frequency of training is not a new topic, but, like everything else, it requires an update from time to time to remind us of basic concepts that may have been diluted along the way and to refocus us to be able to apply what we know in the most effective way possible. The aim of this article is, precisely, to put us in situation of what we know today and how we can distribute our training routines according to the circumstances of each one.

WHAT IS THE IDEAL FREQUENCY FOR EACH PERSON?
There are four points that dictate the ideal training frequency for each of our objectives:

Total days of training per week (availability of each person).
Optimal range of daily sets per muscle group or per movement.
a. In the case of hypertrophy, the rate of protein synthesis,
b. In the case of absolute maximum strength, the accumulation of residual fatigue.
The daily recovery capacity of each individual.

  1. Total training days per week (availability of each person).
    Obviously this is the point that determines in the first place the ability to put in more or less frequency per week and does not depend on theoretical factors of training optimization.

Optimal range of daily sets per muscle group or per movement.
Training volumes greater than about 10 effective sets per muscle per workout are generally more harmful than helpful when training hard and with quality sets [1,2]. At this point, rather than adding more volume per session, training frequency should be increased to accommodate higher training volumes per week (Figure 1).

3a. Hypertrophy and protein synthesis.
In the case of hypertrophy the third factor to consider in establishing an optimal training frequency is protein synthesis. There are strong benefits to be gained from evaluating research results on acute muscle protein synthesis after training and its long-term effect. Muscle protein synthesis correlates positively with muscle mass gains [3-5].

In a strength training session, the fibers of a muscle experience a mechanical load. This mechanical load is detected by mechanoreceptors, leading to anabolic signaling. This signaling triggers an increase in the rate of muscle protein synthesis within each muscle fiber that has been subjected to that overload. That increase in the internal rate of muscle protein synthesis is what causes a higher protein content within the worked muscle fibers and, in the long run, what largely accounts for the increase in muscle size.

Therefore, the length of time during which the rate of muscle protein synthesis is elevated after a workout is quite important and will largely determine the frequency of training per muscle group per week, and is also different between beginners and advanced (Figure 2).

This behavior of protein synthesis determines in part the frequency with which we must expose ourselves to the training stimulus and, consequently, determines the frequency of training. Among all the research that has addressed in one way or another how muscles of different sizes respond to different training frequencies while maintaining volume, the clear and natural tendency is that there is an inverted U-shaped curve that assumes that training the same muscle group two or three times per week is optimal in terms of the volume-frequency-hypertrophy ratio achieved [1,6]. However, when the volume is not equalized, it is shown that increasing the training frequency allows more effective total volume per week to be included and, consequently, the increase in size is greater (Figure 3)

Therefore, depending on the days trained per week and allocated to each muscle group, an average gain of 0.08% per workout could be expected in the case of low frequency and 0.15% per workout in the case of high frequency. Each additional day of frequency increases weekly hypertrophy by 0.11%. That is, each additional day of frequency leads to 22% more hypertrophy, on average [7].

Although high training frequency might seem to imply greater fatigue during the week, we see that, theoretically and objectively, high frequency is superior in the short, medium and long term to low training frequency. The differences are statistically significant in all time frames (short, medium and long term), but in a practical visual way, significant improvements will be noticed in about 12 weeks.

3b. Absolute maximal strength and residual fatigue accumulation.
Due to the very nature of strength adaptations which, we recall, are different at the systemic and peripheral level, the basis for understanding the optimal training frequency differs with respect to a hypertrophy routine and focuses, above all, on improving motor learning and control, reducing antagonist coactivation, and avoiding residual fatigue as much as possible [8].

Thus, the summary of the current literature dictates that, even when volume and intensity are matched, it appears that higher training frequencies lead to greater strength gains [9-12]. This means that distributing a given number of sets over more training days appears to increase strength gains, especially for upper body push exercises (e.g., bench press).

In most analyses, higher frequencies appear to lead to 20 – 25% faster strength gains in both trained and untrained lifters, and there appears to be a fairly linear increase in unit gains from increased weekly frequency up to 4x frequency, however, we do not have enough studies with frequencies above 4x per week to say that beyond that frequency greater improvements are obtained. Therefore, distributing the weekly sets of a given movement over as many days as possible is better for gaining absolute maximal strength than doing it on fewer days.

The explanations behind these results are mainly two:

Greater acquisition of higher skills and motor learning. In general, skills are learned and mastered faster when practiced more frequently.
Increased frequency improves the average quality of training (little loss of speed intraset and between sets). If you have to do three sets of squats in one session, all three sets will probably be pretty good. If you do it twice more in a week, you will have accumulated nine high-quality sets. However, if you were to do all nine sets in a single training session, the quality of those sets would probably start to decline long before you finish your ninth set.
Spreading the weekly sets of a given movement over as many days as possible is better for gaining absolute maximum strength than doing it on fewer days. Increasing frequency improves the average quality of training.

  1. Recovery capacity of each person.
    Each person’s ability to recover is largely determined by training load management and recovery strategies such as more or less daily physical activity, diet, rest, etc.

RECOMMENDATIONS FOR FINDING THE BEST TRAINING FREQUENCY FOR YOU
If you are currently progressing on a low frequency training program (try not to make it frequency I for all muscle groups, although it might be for some, depending on your circumstances, experiences and goals), don’t change anything. However, when you plateau, consider increasing your training frequency.
Many lifters, anecdotally, find that they can tolerate higher frequencies for some exercises or muscle groups, but not for others. Higher training frequencies are worthwhile, but keep in mind that responses are personal and may not reflect the average response.
If you decide to increase training frequency, start by spreading the current training volume over more days per week.
Example: 15 sets of bench presses per week:
15 sets in 1 session,
7 sets in 1 session + 8 sets in another session,
5 sets in 3 different sessions,
4 sets in 3 different sessions + 3 sets in 1 session.

Do not increase the volume until you see how you respond and recover between sessions. It will probably take 3-5 weeks to get an indication of results.
If training exclusively for hypertrophy at a high frequency, consider alternating between more and less demanding exercises for each muscle group. For example, if you do squats on Monday to emphasize quads or knee dominants; do something lighter like press or Bulgarian squat on Tuesday or Wednesday,
Use main and reminder sessions throughout the week for different movement patterns (knee dominants, hips, thrusts, pulldowns…) and intermingle between them. Remember that the total weekly volume is more important than the extreme, acute fatigue of a single session.
Primarily, higher frequencies should be implemented to highlight weak points, or when the weekly volume for a given muscle group is low. Secondarily, to improve on a particular movement.
Depending on the time available each day, consider doing double sessions on some days of the week. Perhaps you can have two 45-minute times of the day that would be more productive in the medium to long term than squeezing in a single 60-minute session per day and using the rest of the free time for other chores. Remember again, to get results you have to keep your mind cool enough to know what you should do (and not just what you want to do at any given time).
Bibliography and references
Schoenfeld, B. J., Grgic, J., & Krieger, J. (2019). How many times per week should a muscle be trained to maximize muscle hypertrophy? A systematic review and meta-analysis of studies examining the effects of resistance training frequency. Journal of sports sciences, 37(11), 1286-1295.
Heaselgrave, S. R., Blacker, J., Smeuninx, B., McKendry, J., & Breen, L. (2019). Dose-response relationship of weekly resistance-training volume and frequency on muscular adaptations in trained men. International journal of sports physiology and performance, 14(3), 360-368.
Brook, M. S., Wilkinson, D. J., Mitchell, W. K., Lund, J. N., Szewczyk, N. J., Greenhaff, P. L., … & Atherton, P. J. (2015). Skeletal muscle hypertrophy adaptations predominate in the early stages of resistance exercise training, matching deuterium oxide-derived measures of muscle protein synthesis and mechanistic target of rapamycin complex 1 signaling. The FASEB Journal, 29(11), 4485-4496.
Hulmi, J. J., Kovanen, V., Selänne, H., Kraemer, W. J., Häkkinen, K., & Mero, A. A. (2009). Acute and long-term effects of resistance exercise with or without protein ingestion on muscle hypertrophy and gene expression. Amino acids, 37(2), 297-308.
Morton, R. W., Murphy, K. T., McKellar, S. R., Schoenfeld, B. J., Henselmans, M., Helms, E., … & Phillips, S. M. (2018). A systematic review, meta-analysis and meta-regression of the effect of protein supplementation on resistance training-induced gains in muscle mass and strength in healthy adults. British Journal of Sports Medicine, 52(6), 376-384.
Schoenfeld, B. J., Ratamess, N. A., Peterson, M. D., Contreras, B., & Tiryaki-Sonmez, G. (2015). Influence of resistance training frequency on muscular adaptations in well-trained men. The Journal of Strength & Conditioning Research, 29(7), 1821-1829.
Nuckols, G. (2019). Training Frequency for Muscle Growth: What the Data Say. https://www.strongerbyscience.com. Retrieved March 15, 2021 from https://www.strongerbyscience.com/frequency-muscle/.
Badillo, J. J. G., & Serna, J. R. (2002). Bases of strength training programming (Vol. 308). Inde.
Grgic, J., Schoenfeld, B. J., Davies, T. B., Lazinica, B., Krieger, J. W., & Pedisic, Z. (2018). Effect of resistance training frequency on gains in muscular strength: a systematic review and meta-analysis. Sports Medicine, 48(5), 1207-1220.
Gomes, G. K., Franco, C. M., Nunes, P. R. P., & Orsatti, F. L. (2019). High-frequency resistance training is not more effective than low-frequency resistance training in increasing muscle mass and strength in well-trained men. The Journal of Strength & Conditioning Research, 33, S130-S139.
Franco, C. M., Carneiro, M. A., de Sousa, J. F., Gomes, G. K., & Orsatti, F. L. (2019). Influence of High-and Low-Frequency Resistance Training on Lean Body Mass and Muscle Strength Gains in Untrained Men. Journal of strength and conditioning research.
Damas, F., Barcelos, C., Nóbrega, S. R., Ugrinowitsch, C., Lixandrão, M. E., d Santos, L. M., … & Libardi, C. A. (2019). Individual muscle hypertrophy and strength responses to high vs. low resistance training frequencies. The Journal of Strength & Conditioning Research, 33(4), 897-901.

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