Discontinuing the Set When You Slow Down on Squats May Boost Strength Gains + Preserve MHC-IIX Fiber Percentage

You want to get rid of those tiny weights and squat big time? Maybe you should watch your squatting velocity... and no, I am not talking about slowing down - rather about keeping your rep speed.
While the headline may suggest that this is yet another article about time under tension, the "speed" I refer to in the headline is only indirectly related to the TUT concept. Rather than that, speed, in this case, refers to the velocity with which you squat... or, to be more precise, the magnitude of repetition velocity loss allowed in each set (20% vs 40%) and its effects on structural and functional adaptations in response to resistance training (RT).

Previous studies have shown that the degree of neuromuscular fatigue induced by RT protocols can be monitored by assessing the repetition velocity loss within a set (Sanchez-Medina. 2011).
Different velocity loss schemes may also be used as part of classic periodization schemes.

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In the study at hand, the scientists did thus use a novel, velocity-based approach to resistance training programming, in which the fixed number of repetitions you have to perform with a given load is replaced by two hitherto largely ignored, closely related variables:
  • the repetition’s mean velocity (how far are you squatting down and getting back up), which is intrinsically related to relative loading magnitude, and
  • the velocity loss to be allowed, expressed as a percent loss in mean velocity from the fastest (usually first) repetition of each exercise set.
In practice this means that you (a) can only select weights with which you can perform the exercise with perfect form at the given speed and (b) you will have to drop the bar, as soon as the prescribed percent velocity loss limit is exceeded - a velocity limit that was set to either 20% or 40% in a recent study from the Pablo de Olavide University (Pareja-Blanco. 2016).
Table 1: Descriptive characteristics of the velocity-based squat training program performed by both experimental groups | Data are mean SD. Only one exercise (full squat) was used in training (Pareja-Blanco. 2016).
The scientists recruited twenty-four young and healthy men (age 22.7 1.9 years, height 1.76 0.06 m, body mass 75.8 7.0 kg)m who volunteered to participate in this study. Their initial 1RM strength for the full (deep) squat (SQ) exercise was 106.2 +/- 13.0 kg (1.41 0.19 normalized per kg of body mass). All subjects were physically active sports science students with a RT experience ranging from 1.5 to 4 years (1–3 sessions/week) and were accustomed to performing the squat exercise with correct technique. The subjects trained twice a week (48–72 h apart) during 8-week for a total of 16 sessions. A progressive RT program which comprised only the squat as the sole exercise was used (Table 1).
"The two groups trained at the same relative loading magnitude (per centage of one-repetition maximum, %1RM) in each session but differed in the maximum percent velocity loss reached in each exercise set (20% vs 40%). As soon as the corresponding target velocity loss limit was exceeded, the set was terminated. Sessions were performed in a research laboratory under the direct supervision of the investigators, at the same time of day ( 1 h) for each subject and under controlled environmental conditions (20 °C and 60% humidity). Subjects were required not to engage in any other type of strenuous physical activity, exercise training, or sports competition for the duration of the present investigation. Both VL20 and VL40 groups were assessed on two occasions: 48 h before (Pre) and 72 h after (Post) the 8-week training intervention. Training compliance was 100% of all sessions for the subjects that completed the intervention" (Pareja-Blanco. 2016).
Pre- and post-training assessments included: magnetic resonance imaging, vastus lateralis biopsies for muscle cross-sectional area (CSA) and fiber type analyses, one-repetition maximum strength and full load-velocity squat profile, countermovement jump (CMJ), and 20-m sprint running - the analysis yielded the following results:
  • The VL20 group trained at a significantly faster mean velocity than those from VL40 (0.69 +/- 0.02 vs 0.58 +/- 0.03 m/s, respectively; P < 0.001), but did sign. less reps [VL40 performed more repetitions (P < 0.001) than VL20 (310.5 +/- 42.0 vs 185.9 +/- 22.2)]. 
  • The mean fastest repetition during each session (that which indicates the relative magnitude of the load being lifted) did not differ between groups (0.75 +/- 0.03 vs 0.76 +/- 0.01 m/s, for VL40 and VL20, respectively) and initial repetition velocities matched the expected target velocities for every training session. 
  • The VL40 group reached muscle failure during 27.0 +/-  4.2 sets (56.3% of total training sets), the VL20 group did not reach failure at all. 
  • Total work was significantly greater for VL40 compared to VL20 (200.6 +/- 47.1 vs 127.5 +/- 15.2 kJ, P < 0.001).
Now based on the often-heard and actually scientifically backed assumption that increases in total volume and training to failure are both conducive to strength gains, we should expect that the VL40 group saw greater increases in muscle size and 1RM strength. This was yet not the case. 
Figure 1: Rel. changes in selected neuromuscular performance variables from pre- to post-training for each group;
p-values indicate the significance of time x group effects, meaning only the inter-group difference in
counter-movement jump performance is statistically significant (Pareja-Blanco. 2016).
Instead, (1) VL20 resulted in similar squat strength gains as VL40, (2) VL20 resulted in greater improvements in CMJ (9.5% vs 3.5%, P < 0.05), and (3) both groups saw identical increases in mean fiber CSA.
Figure 2: Changes in muscle volume for: (a) Whole quadriceps femoris; (b) rectus femoris (RF); (c) vastus medialis (VM); and (d) vastus lateralis plus vastus intermedius (VL+VI | Pareja-Blanco. 2016).
And the above occured in spite of the fact that the VL20 performed 40% fewer repetitions and never reached failure. Can't be? Well, you're right, there's more to the story:"Although both groups increased mean fiber CSA and whole quadriceps muscle volume, VL40 training elicited a greater hypertrophy of vastus lateralis and intermedius than VL20" (Pareja-Blanco. 2016). 
Figure 3: Changes in muscle cross-sectional areas and muscle fiber types percentages, from pre- to post-training for each group, using myofibrillaro adenosine triphosphatase histochemestry; p-values indicate the significance of time x group effects, meaning only the MHC-IIX fiber reduction was sign. different between groups (Pareja-Blanco. 2016).
On the other hand, the VL40 group saw a not exactly strength conducive reduction of myosin heavy chain IIX percentage in the muscle - a change that did not occur in the VL20 group - quite obviously an "endurance" adaptation, the benefit / harm of which would be sport-dependent.
Mo, We, Fr - Sequence of Hypertrophy, Power & Strength Will Up Your Gains on the Big Three (Squat, Bench, Deadlift) / Squat, bench press, deadlift - All major three benefit from the right order in your daily undulating periodization program (DUP) - This is how it works... | learn more
Bottom line: Since this is the first study to probe the effect of two isoinertial RT programs differing in the magnitude of velocity loss experienced during each exercise set on muscle structure and performance, I believe it would be preliminary to draw any conclusions about training in general, but it is unquestionably intriguing that this new way of programming RT regimen in scientific studies did not confirm the classic "higher volume + train to failure = increased gains"-conundrum. Instead, it would appear that using a significant drop in your rep velocity (instead of voluntary failure) as a guide will produce similar size and marginally superior strength gains... at least in trained subjects for the squat exercise.

The latter limitation already reveals: We will need more research to determine how the rep velocity influences the adpatational response to exercise in other subjects, other exercises, training frequencies, intensities, other time-frames and so on and so forth | Comment!
  • Pareja‐Blanco, F., et al. "Effects of velocity loss during resistance training on athletic performance, strength gains and muscle adaptations." Scandinavian Journal of Medicine & Science in Sports (2016).
  • Sanchez-Medina, Luis, and Juan José González-Badillo. "Velocity loss as an indicator of neuromuscular fatigue during resistance training." Med Sci Sports Exerc 43.9 (2011): 1725-1734.
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