Do Intense Workouts Build Muscle?

In resistance training, intensity of exercise can be defined as the strength, power and/or effort that one puts into specific exercises. The word “intensity” in resistance training is more commonly used in relation to the percentage of one-repetition maximum (as much weight that can be lifted correctly one time) that you use during a training session. The higher the percentage of one-repetition maximum (1RM) lifted, the greater the training intensity.

Research has determined that there is a repetition continuum that exists: the higher the percentage of maximum, the fewer the number of repetitions that can be completed. Specific outcomes are strongly associated with the percentage of maximum that is used. This relationship provides valuable information on how to reach a person’s specific performance goals for select fitness and/or training parameters.

Most beginning programs have subjects perform 2 to 3 sets of 8 to 12 repetitions, which correspond to approximately 65% to 80% of 1RM. As training progresses, training intensity can focus on different rep schemes to emphasize use of different energy systems, power and strength (e.g., sets of 6 to 8, sets of 3 to 5, sets of 1 to 3, etc.). These rep schemes and percentages are used to initiate a desired response. Muscular hypertrophy is most closely associated with schemes in the 60% to 85% of max range.

Years and years of research aren’t wrong. Training to failure at 65% to 85% of a 1RM is highly effective in augmenting muscle hypertrophy. When each rep is completed with good form and max effort, the body responds to the training stimulus and will adapt. Pushing your body to fatigue is more than just, “I’m kinda tired; I think I need a rest.” True fatigue should be, “I have nothing left to give,” veins bulging out, ugly lifting faces and full-out maximal effort.

When you take your body to that true burnout, it forces the muscles and the neuromuscular system to work together to start activating and recruiting muscles fibers that weren’t previously used. The body has been created in a way that is ingenious. It doesn’t use every muscle fiber in the muscle belly with each contraction. It only uses what is required to move the weight in order to conserve energy and prevent global fatigue. But if you can get those fibers that have been sleeping to wake up and do some work, once innervated and challenged, they will adapt to being continually recruited, leading to an increase in strength gains.

Typically, the muscle fibers that are used at the higher efforts are going to be Type IIa and IIx muscle fibers. These are your fast-twitch fibers that allow for greater contraction speeds and bursts of force production. Along with these characteristics, these fiber types are highly adaptable and have the greatest hypertrophic potential. Let’s be real – in a world where everyone wants to be bigger, faster and stronger, recruiting more of these guys is pretty advantageous. But along with that, only fibers that are activated can adapt. So if we are able to increase the load and stress on the body to allow for greater recruitment of muscle fibers, there would be an increase in strength.

However, recently conventional wisdom has been challenged. Research has shown that exercise at lower percentages is as effective at impacting hypertrophy. One study investigated the effects of using a lower percentage (30%) of a 1RM to failure compared to using 90% of 1RM, and 30% 1RM work-matched to 90% failure. In this study, participants completed leg extension at various reps to failure. The subjects who performed 30% to failure experienced a greater increase in mRNA expression of MyoD and myogenin, and levels were elevated above the rest 24 hours post-exercise.

In addition, they had an increase in myofibrillar protein synthesis at rest and had a significant increase in the phosphorylation of Erk1/2, p70S6K and 4E-BP1. With more abbreviations than you can shake a stick at, what does all this mean? This study showed that low-load resistance training to failure was more effective in activating acute muscle protein synthesis than high-load low-volume or work-matched. The increases may be due to an increased tension over time on the muscle. It doesn’t take many reps to hit failure when you’re pushing 90%, but when the load is significantly decreased, the muscle has to hold the load for a longer period of time because, where previously it might take 3 or 4 reps to fail, now its 25, 30 or 50 reps.

The increased time of contraction and force production may cause fatigue secondary to just moving the weight up and down, attributing to the overload. You can take this study with a grain of salt and say, “Well, they had acute changes, so what?” Acute changes, if continually placed on the body, can turn into long-term adaptations.

We don’t take creatine only one time and expect it to work its magic long-term. No, if you are anything like me, you take it religiously, knowing that only with a continual dosage do you see benefits. Thus, it appears possible that you can impact hypertrophy at both low-load high-volume and high-load low-volume. So not to be more confusing with all the options you have out there in terms of types of training, but both paradigms appear to work. The take-home point is this: keep your muscles guessing and vary your training.