You pick things up and you put them down again. That is generally how it goes in the gym. You do this, and you will grow. Ok, maybe it’s not that simplistic! But, it’s these two basic movements that will kick off the entire hypertrophy process. After all, picking things up and then putting them down again, is what gets your muscles working, fired up and stressed. This in turn activates a whole host of processes in your muscles to get them repairing and growing back even stronger and bigger (hypertrophy). The process starts again!
Most of the work you do in the gym will be governed by DYNAMIC muscle actions. Dynamic essentially means constant activity (as opposed to STATIC – no change in activity). When you pick things up and put things down, these are dynamic muscle actions: your muscles are constantly changing length so that you can undertake these activities successfully. There are two types of dynamic muscle actions:
⇒Concentric: When the muscle undergoes a concentric contraction it shortens. The contractile elements of the muscle come together (overlap) and allow the muscle to produce the necessary force (force produced by muscle is large enough to overcome the external load).
⇒Eccentric: During an eccentric contraction* the muscle lengthens. Eccentric contractions act to decelerate a joint in order to control the position of the external load (the external load is greater than the force produced by the muscle).
*Contraction DOES NOT ALWAYS IMPLY SHORTENING (as in an eccentric contraction).
⇒A static muscle action would be a isometric: Muscle produces force while maintaining a constant length.
What Type Of Dynamic Muscle Action Produces Greater Hypertrophic Responses?
Although we are constantly performing two types of DYNAMIC muscle actions in the gym, it’s not quite clear which of the two actually produces GREATER responses in hypertrophy. So what has the science told us up until now?
Farthing and Chilibeck (2003) conducted a study with 24 untrained volunteers, which underwent either fast or slow velocity training. They underwent 8 weeks of training one arm eccentrically (ECC), followed by another 8 weeks concentric (CON) training with the other arm. 10 subjects served as controls.
⇒The results? After each 8 weeks of training, greater levels of elbow flexor muscle thickness (hypertrophy) were found in the ECC training group in comparison to the CON training group. There were no significant changes in strength or hypertrophy in the control group. Furthermore, fast ECC training resulted in greater levels of hypertrophy than the fast CON and slow CON training. Also, slow ECC resulted in greater hypertrophy than fast CON training. The ECC fast training resulted also in the greatest strength improvements.
⇒The conclusion? That eccentric muscle actions produce the greater strength and hypertrophic responses in comparison with concentric muscle actions.
Friedmann et al (2004) conducted a study in 18 untrained males, which underwent 4 weeks of low-resistance, high-repetition knee extension exercise. 9 of the participants underwent concentric training with a leg curler machine with loads equivalent to 30% of the concentric 1RM. The other 9 participants underwent eccentric training with a computer driven device, with the concentric load set at 30% of the concentric 1RM and the eccentric load equivalent to 30% of the eccentric 1RM.
⇒The results? It was found that increases in peak torque and muscle cross sectional area were significantly greater in the eccentric training group over the concentric training group.
⇒The conclusions? Training with eccentric loads leads to greater increases in muscular strength and hypertrophy in comparison to training with concentric loads.
Norrbrand et al (2008) published in a study in which 15 healthy untrained men underwent a 5 week training program consisting of either 4 sets, 7 repetitions of a concentric-eccentric coupled knee extensions 2-3 times weekly (concentric training group) or, using a flywheel device, which provides for increasing amounts of eccentric overload.
⇒The results? Greater increases in hypertrophy of the quadriceps were observed in the eccentric training group compared with the concentric training group.
⇒The conclusion? That an eccentric load provides a more potent stimulus for inducing muscular hypertrophy in comparison to a concentric load.
The bottom line: From these studies, it shows clearly that eccentric muscle actions promote superior increases in muscle mass compared to concentric muscle actions.
⇒An important question to ask is: how might eccentric muscle actions promote superior increases in muscle hypertrophy over concentric muscle actions? What is happening in terms of physiological processes (signalling, protein synthesis, enzymatic activity etc.), to drive these superior eccentric-induced hypertrophic responses?
A Potential Model For Eccentric-Induced Hypertrophy?
Interestingly in a study published by Moore et al (2005), it was found that those untrained men who underwent eccentric leg training, exhibited faster rises in muscle protein synthesis following training in comparison to those who underwent concentric training. They suggested that this faster rise in muscle protein synthesis could result in more protein accretion and muscle hypertrophy during chronic resistance training utilising maximal eccentric muscle actions.
Shepstone et al (2005) also provided some insight into why these eccentric actions might lead to greater increases in muscle cross sectional area over concentric actions. They suggested it might have something to do with greater extents of protein remodelling that take place during eccentric muscle actions (*an indicator for this was Z-line streaming).
In another study by Eliasson et al (2006), it was found that maximal eccentric concentrations (but not sub maximal eccentric or maximal concentric contractions) elicited increases in the activity of anabolic singling processes. This is likely to contribute to the greater increases in hypertrophy seen with eccentric muscle actions.
In a recent paper published by Ogborn et al (2017), it was suggested that eccentric muscle actions cause a greater degree of exercise-induced muscle damage. This can lead to changes in the structural integrity of the muscle itself (through alterations in supportive, contractile and structural elements). Since one can withstand greater loads during eccentric muscle actions, it’s not surprising that muscle damage is greater! This is likely to cause an increase in a range of anabolic signalling processes to allow for repair and strengthening of the damaged muscle tissue.
*Z-line streaming: The Z-lines are found at the edges of the sarcomere. Essentially, these are the basic building blocks that make up all muscles. Each sarcomere contains the contractile elements of the muscle. When the structure of the Z-lines change they begin to ‘drift’ apart (‘streaming’) disrupting the structural arrangement of the sarcomeres. This can be due to changes in proteins which are found at the Z-lines. Hence, a greater degree of Z-line streaming signifies a greater degree of protein remodelling.
Most of the time, people tend to focus more on the ‘concentric’ part of a movement rather than the eccentric. Typically, the idea has mostly been that concentric is where the most muscle gains come from. For instance on a bench press, people focus more on the push up of the bar from the chest into the air (rather than on the eccentric lowering to the chest). Or, take a barbell or dumbbell row. People focus on that ‘tight concentric contraction’ (bringing the dumbbell or barbell towards your chest) rather than on the lowering of the barbell or dumbbell towards the ground (eccentric).
⇒Given these findings, it might actually be the case that the eccentric part of a movement provides greater hypertrophic responses, possibly through increased exercise-induced muscle damage and subsequent anabolic signalling processes (although this connection still needs further research).
If you ask me, it seems that focusing on both concentric and eccentric muscle actions in your workout, might provide the best training stimulus for ultimate size and strength development.
Any questions, ask away!