Training frequency can be defined as the number of times a particular exercise or body part is trained over a specified period of time (Schoenfeld, Ogborn, & Krieger, 2016). During a synthesis of the current limited number of scientific studies, Schoenfeld et al. (2016); Schoenfeld, Ratamess, Peterson, Contreras, and Tiryaki-Sonmez (2015) recommended the periodization of training frequency over a multiple training cycles. This recommendation is based on the lack of significant differences in hypertrophic adaptations when volume is equated between muscle groups. The authors demonstrated positive adaptations in hypertrophy using a single session vs 2 and 3 sessions with equal volumes performed per muscle group per week.
An important consideration extrapolated from Schoenfeld et al. (2016); Schoenfeld et al. (2015) is that hypertrophy benefits are volume/workload related. Schoenfeld (2010) reviewed the mechanisms of muscular hypertrophy and summarised the 3 determining factors as: muscular tension, muscle damage and metabolic stress. Muscular tension requires an adequate load above a threshold be applied to the active musculature in order to stimulate hypertrophy. However, this load must enable sufficient volume to be lifted in order to create sufficient muscle damage and metabolic stress. Taking an individual with a 1RM back squat of 100kg, this individual could lift 100kg and maximise the mechanical tension on the active musculature. However, they would be able to lift this load for only 1 rep and multiple sets would induce a large amount of neuromuscular fatigue that could lead to over-training if maintained over a long period of time (indicating the need for appropriate periodization of training load).
Using a load of 70-75%1RM or approximately a 10RM load would enable the individual to lift this load for 10 reps in 1 or more sets leading to a volume-load (load x repetitions) of 750kg in 1 set compared to a volume load of 100kg (1set x 100kg). 10RM has been indicated as sufficient to induce hypertrophy via muscular tension (Stone, Stone, & Sands, 2007). This load also facilitates greater potential for muscle damage and metabolic stress through exposure to higher volumes of sufficient muscular tension.
It is likely that the previous studies by Schoenfeld et al. (2016); Schoenfeld et al. (2015) are accurate with the suggestion that differences in higher and lower training frequency groups when volume-equated are non-significant (p>0.05). Although the current body of literature is sparse, the suggestions are logical based on mechanistic and physiological principles (Schoenfeld, 2010; Stone et al., 2007). Coaches should therefore pay attention to volume-load when attempting to induce muscular hypertrophy. This can be calculated per body part or exercise over the course of a session, week, mesocycle, macrocycle and multiple macrocycles. The aim should be to organise progressive variations in volume load while maintaining training load within the 6-12RM range (Haff & Triplett, 2016).
From a practical perspective, training frequency will be naturally increased as a result of session-by-session timing restrictions. As the testosterone-cortisol ratio decreases after 1-1.5 hours of training it is advisable to maintain individual sessions at 90 minutes and increase the frequency of training in order to achieve larger volumes of training (Turner, Comfort, Moody, & Jeffreys, 2010). This can be in the form of a 30-60 minute break between sessions (split sessions) or by increasing the number of training sessions per week.
Putting this in perspective, if an athlete needs to lift a volume load of 10,000kg in the back squat in 1 week it is not advisable to achieve this is one session but split this into multiple more manageable sessions (eg 5 sessions of 2000kg, 2x5000kg, 4x2500kg). Looking more deeply at the 4x2500kg session and considering an athlete who can lift 100 for 8-12 reps and is feeling slightly drained from a previous session. This athlete could programme the following as a part of an individual session: back squat 3sets x 8-9reps @100kg with an aim of 2500kg for the session. The purpose of the pre-fatigue load is to facilitate performance in the additional 4 sessions while limiting dramatic increases in fatigue.
The athlete above would certainly not be able to achieve a volume load of 10,000kg in 1 session (~100 reps at 100kg). However, to achieve progressive increases in hypertrophy it may be necessary to introduce higher frequencies of training to more effectively distribute workload at these more advanced stages of training.
Coaches and athletes interested in inducing hypertrophy should be concerned with organising progressions and variations in volume-load while working within recommended intensity ranges over the course of training. Volume load targets can be measured per session, day, week, mesocycle, macrocycle and over multiple macrocycles and should be varied appropriately while providing time for recovery through reduced volume-load sessions/days/weeks. Training frequency per week should be increased as a natural part of the progression of weekly volume load. It becomes necessary at higher volume loads to increase the number of sessions per week to avoid intra-session fatigue-induced decreases in testosterone-cortisol ratio.
Haff, G. G., & Triplett, T. N. (Eds.). (2016). Essentials of strength and conditioning (4th ed.). Champaign: Human Kinetics.
Schoenfeld, B. J. (2010). The mechanisms of muscle hypertrophy and their application to resistance training. The Journal of Strength & Conditioning Research, 24(10), 2857-2872.
Schoenfeld, B. J., Ogborn, D., & Krieger, J. W. (2016). Effects of Resistance Training Frequency on Measures of Muscle Hypertrophy: A Systematic Review and Meta-Analysis. Sports Medicine, 1-9.
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.
Stone, M. H., Stone, M., & Sands, B. (2007). Principles and practice of resistance training: HUMAN KINETICS PUB Incorporated.
Turner, A., Comfort, P., Moody, J., & Jeffreys, I. (2010). Neuroendocrinology and resistance training in adult males. Professional strength and conditioning(17), 15-24.