Go Slow to Grow: Almost 3x Bigger Biceps W/ Slow Reps

Beware: Results could differ for e.g. legs.
12 weeks of "[r]esistance training [of the elbow flexors = biceps] with slow speed of movement is better for hypertrophy and muscle strength gains than fast speed of movement," that's the title and conclusion of a recent study from the Federal University of São Paulo (Pereira. 2016), a results that may surprise those of you who have been seeing people in the average youtube training motivation video repping out 15 reps in 15 seconds.
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Bullshit? Idiots? Well, previous studies into the link between the speed of repetitions in isokinetic exercise and people's gains actually found that fast speed provides greater strength gains and muscle hypertrophy than the slow speed:
  • Morrissey, et al. (1998) compared squatting at 25 to 125 deg/sec and found that both training groups "improved similarly in many variables with training but also showed some differences [but in] the long jump, the fast group was superior in numerous variables including knee peak velocity and total-body vertical and absolute power" (Morssey. 1998).
  • Pareja-Blanco, et al. (2014) found comparable results when comparing maximal to 50% maximal velocity squatting 16 years later, when the analysis of their experimental data from 21 resistance-trained young men who were randomly assigned to a MaxV (n = 10) or HalfV (n = 11) group and trained for 6 weeks using the full squat exercise, found that MaxV "may provide a superior stimulus for inducing adaptations directed towards improving athletic performance" (Pareja-Blanco. 2015).
One thing you have to keep in mind when interpreting these results is that the researchers main interest was in common athletic performance where the ability to contract your muscles not just forcefully, but also and often predominantly fast matter. The increased time under tension and any potential adapatational benefits, on the other hand, may - in the lon run - be more important for hypertrophy and strength gains:
Figure 1: Myofibrillar, mitochondira and sarcoplasma fractional protein synthesis (Burd. 2012).
Burd, et al. (2012), for example, were able to show that "t the time the muscle is under tension during exercise may be important in optimizing muscle growth; this understanding enables us to better prescribe exercise to those wishing to build bigger muscles and/or to prevent muscle loss that occurs with ageing or disease" (Burd. 2012) - a conclusion that is yet, as the acute protein synthesis data in Figure 1 goes to show you based on predictions that did not take into account potential increases in muscle breakdown. Pereira et al. are thus right, when they demand that further studies are necessary - not just, but specifically, in already trained individuals.
What is "isotonic training"? And how fast / slow are "fast" and "slow" Sounds funky, but is just the regular strength training method where you contract your muscles to lift an object over a specific range of motion and at a constant resistance. It is used to both strengthen muscles and increase flexibility in joints. In this particular instance, the subjects trained 2 times a week, always respecting minimum 48-hour interval between stimuli. They performed 3 sets of 8 repetitions maximum of scott curls, increasing the weight whenever they could do more than 8 reps. Rest interval between sets was of two minutes. Cadence differed between 1s in the concentric phase, 0s in the transitional phase from the concentric for the eccentric phase, 1s in the eccentric phase and 0s in the transitional phase from the eccentric to the concentric phase (1010) in the fast (FS) group and 1040 in the slow (SS) group.
Of the latter, the scientists recruited a dozen, i.e. 12 healthy adults with at least 1 year of resistance training experience and no use of sports supplements or anabolic agents, who were randomly assigned into two groups: fast speed (FS) and low speed (SS) for 12 weeks.
Figure 2: Fast and slow strength training affect the strength and size response of trained men differently (Pereira. 2016).
Muscle hypertrophy was measured by an ultrasound examination of the cross-sectional area of the brachial biceps muscle. Fat mass was assessed by the means of calipers only once. Muscular strength was verified by 1 RM test, likewise before and after.

To check the possible differences in strength and hypertrophy between pre and post training and between groups there were compared by two-way ANOVA for repeated measurements and the effect size (ES) was calculated and the results are quite unambiguous:
  1. Improvement in the cross-sectional area (P=0.019) and muscular strength (P=0.021) in the SS group between pre and post training was verified. 
  2. The SS group had bigger effect sizes than FS group for hypertrophy and strength from pre to post training. 
  3. SS training was more effective to improve hypertrophy and muscle strength in well-trained adults.
In other words: the slow reps were significant strength and size builders, while the rapid movements were not. That neither of them made the subjects grow hilariously, on the other hand, shouldn't be surprising - you can't expect to keep your "rookie gain-rate" of a pound per week for more than the first weeks... bad news, I know.
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What's the advantage of going slow? Practically speaking "going slow will make you grow", but the underlying mechanism is not as simply as this summary would suggest. There's first of all the previously illustrated increase in protein synthesis (see Figure 1; Burd. 2012).

Furthermore, Paulo Eduardo Assis Pereira and colleagues believe that the pump or rather the increased compression / time of compression of the blood vessels may lead to vascular occlusion, build up of metabolic debris and positive / adaptive stress / stressors, which in turn could explain the augmented hypertrophy response.

Accordingly, the authors ascribe the corresponding strength increase to skeletal muscle hypertrophy. That is in contrast to the concept of "move as fast as possible independent of the resistance" which is believed to benefit strength development directly - esp. in the early weeks via neural adaptation (Cormie. 2011). Eventually, Pereira et al. are may yet be right to ultimately suggest that a "variety of stimulus in periodization is needed to optimize resistancetraining programs" (Pareira. 2016) | Comment on Facebook!
  • Burd, Nicholas A., et al. "Muscle time under tension during resistance exercise stimulates differential muscle protein sub‐fractional synthetic responses in men." The Journal of physiology 590.2 (2012): 351-362.
  • Morrissey, Matthew C., et al. "Early phase differential effects of slow and fast barbell squat training." The American journal of sports medicine 26.2 (1998): 221-230.
  • Pareja-Blanco, F., et al. "Effect of movement velocity during resistance training on neuromuscular performance." International journal of sports medicine 35.11 (2014): 916-924.
  • Pereira, Paulo Eduardo Assis, et al. "Resistance training with slow speed of movement is better for hypertrophy and muscle strength gains than fast speed of movement." International Journal of Applied Exercise Physiology 5.2 (2016): 37-43.
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