Effect of Repetition Duration—Total and in Different Muscle Actions—On the Development of Strength, Power, and Muscle Hypertrophy: A Systematic Review
Moreno-Villanueva, Adrián MD; Pino-Ortega, José PhD; Rico-González, Markel PhD
Strength and Conditioning Journal: October 2022 - Volume 44 - Issue 5 - p 39-56
To analyze how muscle activation duration (MAD) – essentially the amount of time muscle is active during a complete repetition - affects the development of strength, power, and hypertrophy. Each repetition is divided into the:
1. Eccentric (ECC, lowering) phase.
2. Isometric/turn around (ISO-TURN, isometric stop-switch in direction) phase.
3. Concentric (CON), raising) phase.
4. Isometric/pause (ISO-PAUSE, isometric stop-pause between reps) phase.
ECC --> ISO-TURN --> CON --> ISO-PAUSE
A 4-digit nomenclature was also adopted to describe the duration of the repetition by each segment: 4/0/2/0 = :08
1st digit = ECC (:04 in the example).
2nd digit = ISO-TURN (:00 in the example).
3rd digit = CON (:02 in the example).
4th digit = ISO-PAUSE (:00 in the example).
· An “explosive muscle action” is one developed at the maximum volitional speed.
· A “fast muscle action” is one of a duration of :01 to :02.9 seconds (i.e., 2/0/.5/0).
· A “medium muscle action” has a duration of :03–:05.9 seconds (i.e., 2/1/2/0).
· A “slow muscle action” a duration of :06–:09.9 seconds (i.e., 4/1/2/1).
· An “extremely slow muscle action” a duration of more than :10 seconds (i.e., 8/0/4/0).
The results showed that protocols with medium ECC MAD and fast CON MAD - specifically cadences 2 to 4/0/1/0, produced the highest improvement values for the development of maximum dynamic strength in both trained (18–24%) and untrained subjects (10–14%).
For the development of maximum power, a medium total repetition MAD of less than 4 seconds and slow total repetition MAD, less than 8 seconds, seems suitable for untrained and trained subjects, respectively, with the condition that CON MAD is explosive or fast (cadence 4 to 8/0/max to 3/0).
For muscle hypertrophy it could be improved with a total repetition MAD less than 8 seconds in both trained and untrained subjects.
In conclusion, the prescription of the MAD, total and phase specific, should be planned according to the adaptations desired in untrained and trained individuals.
The repetition duration is one of the RT parameters whose manipulation can optimize the development of maximum strength. The repetition cadences 3/0/1/0 and 4/0/1/0 reported the greatest magnitude improvements, both in trained subjects +18% and +24%, respectively and untrained +10% and +14%, respectively. These improvements were of greater magnitude predictably due to their greater optimization in the recruitment of muscle fibers.
It was found a greater significant increment in maximal dynamic strength and relative strength in those subjects who performed a cadence of 1 to 2/0/1 to -2/0 with a 6 to 10-1RM compared to those subjects who followed an extremely low speed training prescription (4 to 5/0/10/0 with the 6 to 10-RM) and endurance training at medium total repetition MAD (1 to 2/0/1 to 2/0 with a 20 to 30-RM.
It was investigated to determine the effect of different CON MAD and found that explosive CON muscle actions lead to greater improvements (+18.2%) in maximal dynamic strength compared with concentric muscle actions developed at twice the time of maximum concentric speed (+9.7%). This could be caused by a higher movement velocity that induces a greater implication of type IIX muscle fibers and subsequent development of maximal dynamic strength.
On the other hand, when investigating the effects of both CON and ECC in maximal dynamic strength it was found that the use of 4/0/1/0 and 3/0/1/0, respectively, induced greater improvements (+18-24%) than in the 1/0/1/0 control group.
Therefore, the use of fast CON MAD with medium ECC MAD (3 to 4/0/1/0) could be a suitable strategy to be considered with trained subjects to retain elastic energy in the ECC to transfer it to the subsequent CON.
In brief, fast CON MAD in combination with medium ECC MAD (3-4/0/1/0) can induce greater improvements in maximal dynamic strength in both trained and untrained subjects due to the ability of ECC muscle actions to produce higher peaks of strength with lower neural activation and metabolic cost as compared to CON muscle actions.
Power depends closely on the force-velocity relationship. Therefore, an exercise prescription based on explosive efforts and intentional total repetition MAD using a moderate–submaximal load intensities (60–80% of 1-RM) makes sense.
The main findings suggest that the training prescription should be between 60 and 95% of 1-RM depending on the current training level, with a medium total repetition MAD of less than :04 for untrained subjects (60–80% of 1-RM and 2/0/2/0) and a slow total repetition MAD of less than :08 for trained subjects (60–95% of 1-RM and the condition that CON MAD is fast and less than :02.
Regarding movement velocity it was found that a CON MAD equal to the ECC MAD (i.e., 1 to 2/0/1 to 2/0) induces improvements in power along with a greater recruitment of type II fibers (+23% type IIA; +30% type IIAX) when training at higher speeds, but that decreases in the percentages of type IIX muscle fibers at that same cadence.
It was found that the group with a MAD of 6/0/2/0 obtained a significant decrease (−15%; p. <0.05) in the percentage of type II fibers and an increase (+10%; p. <0.05) in type I fibers, whereas the group with a MAD of 2/0/6/0 - although not reducing the percentage of type I fibers - achieved an increment (+7%; p. >0.05) in the percentage of type IIA fibers.
In untrained subjects, the use of between 60 and 80% of 1-RM is suggested with a medium total repetition MAD of less than 4 seconds.
For trained subjects, maximum power can be obtained with total repetition MAD of up to 8 seconds provided that CON MAD is fast (< :02) and ECC MAD does not exceed :08.
In investigations that analyzed this parameter in training cadences of CON MAD equal to ECC MAD - reflecting increases in counter movement jumping (CMJ) values in untrained (+8.5%) and trained (+4%) subjects - with significant increases (+10%) in maximum and average power in the latter.
Improvements in power production were also reported at speeds lower than 0.8 m/s (+36%) (21) and 1 m/s (+18%) (46) in studies that investigated this parameter in groups of trained subjects performing explosive contractions.
Because the use of different MAD for both CON and ECC could lead to different physiological regulations and morphological adaptations it would be useful to summarize what MAD should be prescribed to induce greater muscle hypertrophy in untrained and trained subjects.
The consensus of comprised a total repetition MAD of between :04 and :14 with most of the investigations with a total repetition MAD of less than 7 seconds for muscle hypertrophic improvements as long as muscle failure is reached. However, MAD in each phase of muscle action (CON and ECC) seems to be crucial in hypertrophic developments.
It was found that a regimen of 4/0/10/0 augments cross sectional area (CSA) of fiber type II (+11-16%) as compared to a regimen of 1 to 2/0/1 to 2/0 focused on endurance training.
Other studies showed greater improvements in muscle thickness (+6-18%) in untrained subjects who used fast–moderate total repetition MADs, and improvements of a greater magnitude when ECC MAD was greater than CON MAD (6–10% in 3/0/3/0 vs. 15–18% in 2–4/0/1/0) which support the hypothesis of the greater capacity for tolerance and accumulation of mechanical tension (i.e., explosive CON muscle action) of ECC MAD.
For trained subjects, evaluation of the effects of different training prescription protocols on muscle CSA using 2/0/6/0 and 6/0/2/0 as compared to 1/0/1/0 and 4/0/1/0. It found that using a MAD of between :05 and :08 seconds showed significant improvements (+11-25.8%).
Significant improvements in muscle thickness were reported in groups with repetition cadences with ECC MAD greater than CON MAD, of a considerably higher magnitude in untrained subjects (15–18%) compared to trained subjects (+3%) when using similar repetition cadences (4/0/1/0 and 3/0/1/0, respectively).
Finally, muscular cross-sectional area (CSA) adaptations were extensively studied in both population groups. The highest values of CSA were recorded in the training cadences with ECC MAD equal to CON MAD (+3.4-27.0%) in untrained subjects with the higher values in cadence 1 to 2/0/1 to 2/0 and those in which CON MAD was greater than ECC MAD (+4.3-25.8%) with the higher values in cadence 2/0/6/0.
In summary, it is suggested that hypertrophic muscle improvements in untrained subjects can occur with a total repetition MAD of up to :14 although above :08 these improvements are of a lesser magnitude.
Muscle strength = medium ECC MAD and fast CON MAD (3-4/0/1/0) could be considered to improve maximal dynamic strength independently of the training status of the subjects.
Power = an explosive CON muscle action is highly recommended to maximize improvements in this outcome, accompanied by medium (<:04) and slow (<:08) ECC muscle actions in untrained and trained subjects, respectively.
Hypertrophy = a total repetition MAD less than :08 allows for hypertrophic improvements in both trained and untrained subjects