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In a study looking at age affects of Protein Synthesis (6) it was noted that by the end of 2 weeks of weight-lifting exercise, MHC and mixed protein synthesis rates increased in both younger and older participants. The actin protein synthesis rate was increased after exercise in only the younger group. The magnitude of the exercise-induced increase in MHC and mixed protein synthesis rates was similar in the younger and older groups. In the younger group, the MHC and Actin (contractile) protein synthesis rate increased 83% and 78% respectively while the mixed muscle protein synthesis rate increased (102%). This study points to the identification that, as with feeding, all proteins are up regulated with resistance exercise. Now the interesting point was that the exercise protocol used seven weight-lifting exercises (Nautilus equipment) that included the chest press, inclined chest press, latissimus pull-down (wide and narrow grip), leg press, knee extension, knee flexion, and two free weight-lifting exercises that included seated overhead press and overhead triceps extension. Each participant completed ten weight-lifting exercise sessions: 2–3 sets/day of the nine exercises listed above, 8–12 repetitions/set, 60–90% of maximum voluntary muscle strength. This was a pretty broad range of intensity and easily points out that the rep range itself isn’t the determining factor.
To further illustrate that the intensity or rep range utilized does not change this ratio all too dramatically we can look at more recent work looking into the synthetic rates of fractional proteins with dynamic or resistance type exercise.
Atherton et al. (7) used electrical stimulation with high frequency (HFS; 6x10 repetitions of 3 s-bursts at 100 Hz to mimic resistance training) to identify signalling present during increased protein synthesis. What he noted, significant to this article and discussion, was that HFS significantly increased myofibrillar and sarcoplasmic protein synthesis 3 h after stimulation 5.3 and 2.7 fold, respectively.
Interestingly Bowtell (8) found that when the same total amount of ATP is turned over, exercise at 60, 75 and 90% of the one-repetition-maximum force results in exactly the same stimulation of muscle protein synthesis, suggesting that once all muscle fibers are recruited increases in tension above 65% cause no further stimulation in muscle protein synthesis. Even though I am not aware if the specific fractions were measured in the Bowtell study it would stand to reason that in light of the previous both fractions would be up regulated.
In another study, Louis (9) subjects carried out 20 series of 10 repetitions (with a rest of 80 s after each series) on an isokinetic dynometer to evaluate if Creatine has an impact on anabolic signalling and protein synthesis. Again, in the realm of this article, what was found interesting was that this exercise increased the synthetic rates of myofibrillar and sarcoplasmic proteins by 2- 3 fold.
Looking at dynamic exercise (one legged kicking), Miller (10) saw that the rates of protein synthesis in the exercised leg increased substantially by 6 h and peaked within 24 h in both myofibrillar and sarcoplasmic fractions, i.e. increases of 2.8 and 2-fold, respectively. The rates of myofibrillar and sarcoplasmic protein synthesis in the exercised muscle had fallen slightly by 48 h but were still significantly above the rates in the rested leg. By 72 h, the rates of both fractions had decreased.
Our last look at fractional elevations will look at whether or not there is a fiber type dependency. In many animals the rate of protein synthesis is higher in slow-twitch, oxidative than fast-twitch, glycolytic muscles. To find if this held true for muscles in the human body a recent study (11) recruited nine healthy, young men and with a constant infusion looked at synthetic rates in the soleus, vastus lateralis and tricep. Type-1 fibers contributed 83 +/- 4% (mean +/-s.e.m.) of total fibers in soleus, 59 +/- 3% in vastus lateralis and 22 +/- 2% in triceps. The basal myofibrillar and sarcoplasmic protein fractional synthetic rates (FSR, % h(-1)) were 0.034 +/- 0.001 and 0.064 +/- 0.001 (soleus), 0.031 +/- 0.001 and 0.060 +/- 0.001 (vastus), and 0.027 +/- 0.001 and 0.055 +/- 0.001 (triceps). During amino acid infusion, myofibrillar protein FSR increased to 3-fold, and sarcoplasmic to 2-fold above basal values (P < 0.001), again showing that even within differing types of muscle tissue the ratio remains.
What can be seen when reviewing these and many other papers on the subject is the response to resistance training of fractional elevation remains in line with the results of feeding, both are elevated but the slower turnover proteins (myofibrillar) generally show a larger magnitude in increase. Since these studies show that this holds true with resistance training, dynamic exercise and HFES, all utilizing differing intensities and work output, it seems unlikely that the rep range is the sole cause of any increase in sarcoplasmic fraction up-regulation.