Eccentric Exercise "Superior Driver of Acute Anabolic Signalling That May not be Mirrored in the Rate of Muscle Protein Synthesis", 12 Week Human Study Suggests

Concentration curls are one of the few exercises, where eccentrics make sense. They are safe and you can even do them if you don't have a training partner.

The title of today's SuppVersity article is actually an almost literal quote from the abstract of a recent paper from the Aarhus University that's about to be published in an upcoming issue of the peer-reviewed scientific journal Amino Acids, where it says: "In conclusion, maximal eccentric contraction mode may constitute a superior driver of acute anabolic signalling that may not be mirrored in the muscle protein synthesis rate."

Quite an intriguing conclusion that puts yet another huge questionmark behind the usefulness of the three dozen of studies that measure exclusively (acute) protein synthesis to assess the efficacy of certain exercise and/or supplementation regimen.

Before we get caught up in discussing the implications of the study at hand (as we are going to see later, we would be jumping to conclusions, anyways), it would yet be wise to take a closer look at the data that's at the heart of the previously cited conclusion.

Rahbek and her colleagues from the University of Aarhus and the University of Copenhagen set out to confirm the following hypothesis (Rahbek. 2014):

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   In the exercise-habituated state, single-bout  eccentric contractions would augment muscle protein synthesis and mTOR signalling compared to concentric contractions
2. The effects would be amplified if the subjects consume whey protein hydrolysate and carbohydrates after the workout compared to carbohydrates, alone.
3. Compared to the concentric training, the eccentric training would provide a stronger hypertrophy response and a more sustained increase in proteins involved in the mTOR protein synthetic cascade.

Luckily the Danish researchers did not content themselves with measuring the acute response to a single exercise, but used the funds they received from Arla Foods Ingredients group wisely and recruited twenty-four young healthy recreationally active men (height, 1.82  ±  0.015  m; weight, 78.1  ±  1.8  kg; age, 23.9 ± 0.8 years; fat %, 16 ± 0.9 %) as their study subjects for a 12-week study with (1) a short period of exercise habituation, (2) a single-bout resistance exercise trial to investigate the acute phase exercise responses, and (3) a 12-week training period to investigate accumulated resistance exercise responses.

"All participants per formed eccentric work (ecc) with one leg and concentric work (cOnc) with the other leg. eccentric exercise was randomly ascribed to either the dominant (preferred kick ing leg) or the nondominant leg to exclude any potential pre-training differences between the legs." (Rahbek. 2014)

In addition, the effects of a WPH +cHO supplementation versus isocaloric cHO supplementation were investigated in the single bout trial and the training period. The participants were randomly divided into one of the two supplement groups and supplements were provided in a double blinded fashion. this within-participant design with regard to contrac tion mode was used to minimize the potential differences in the training response that are inherent with group designs because of differences in initial training, nutritional and hormonal status. Accordingly, the following four inter ventions were compared: (I) eccentric training with WPH + CHO; (II) eccentric training with CHO only; (III) conencentric training with WPH + CHO, and; (IV) concentric training with CHO.
Throughout the study period, the participants were instructed to maintain their normal habitual physical activity level and dietary intake. Three days prior to the start of the study, the participants were asked to refrain from physical exercise. One basal muscle biopsy was then sampled from a randomly chosen leg. The biopsy was repeated twice: Three days after the 7-day habituation phase, and 3-6 days after the last training session 12 weeks later.

"Each participant completed 2–3 exercise sessions per week over a 12-week period to a total of 33 training sessions. All exercise sessions were initiated with 5 min light bicycling warm-up. Eccentric load was aimed at 120 % relative to concentric loading, with a training supervisor assisting to allow isolated exercise modality of the two legs. the load difference is parallel to the approximate strength difference between slow ecc[entric] and con[centric] contractions during isokinetic strength testing." (Rahbek. 2014)

Unfortunately, the resistance training program consisted of isotonic knee extensions, only (understandable from a science perspective, but disappointing for all of us who would have preferred a more realistic training scenario). The latter were performed with the following set × repetitions:

Figure 1: Sustained elevations in anabolic signalling were observed only in the eccentric training group.

• 6 × 10– 15 rM (sessions 1–4),

• 8 × 10–15 rM (sessions 5–10),

• 10 × 10–15 rM (sessions 11–20), 

• 12 × 6–10 rM (sessions 21–28), and 

• 8 × 6–10 rM (sessions 29–33) 

The participants were instructed to perform the exercise with picture perfect form and at a tempo of 2 seconds on both the concentric and the eccentric phase of the exercise. Two minutes of recovery were interspaced between sets and all training sessions were closely supervised and monitored by qualified training instructors to ensure proper execution and loading.

Figure 2: Changes (%) in quadriceps CSA over the 12-week training period (Rahbek. 2014)

In spite of its minimalist nature, the training program elicited measurable increases in muscle size, which were significantly more pronounced, when the subjects consumed 0.30g/kg whey protein hydrolysate and 0.30g/kg carbohydrates, instead of 0.60 g/kg carbohydrates (CHO trial) after the workout (see Figure 2).
References:

• Aagaard, Per, et al. "Neural inhibition during maximal eccentric and concentric quadriceps contraction: effects of resistance training." Journal of Applied Physiology 89.6 (2000): 2249-2257.
• Rahbek et al. "Divergent resistance exercise contraction mode and dietary supplementation type on anabolic signalling." Amino Acids (2014). Ahead of print.