Influence Of Muscle Contraction Intensity And Fatigue On Muscle Protein Synthesis (MPS) Following Resistance Exercise Burd, Nicholas A.; West, Daniel WD; Staples, Aaron W.; Holwerda, Andrew M.; Moore, Daniel R.; Tang, Jason E.; Baker, Steven K.; Phillips, Stuart M. Volume 41(5) Supplement 1, May 2009, p 149 PURPOSE: To determine how changes in mixed skeletal muscle protein synthetic rate (MPS) are influenced by training load (90 vs. 30% maximal strength) or exercise intensity (failure vs. work matched) over 24h of recovery. METHODS: Six male subjects (21±1y, 176±1cm, 74.5±2.7kg) were counterbalanced and randomly assigned to two of three unilateral exercise conditions (n = 4 each group) consisting of 4 sets at 90% 1RM to failure (90RM), 30% 1RM worked matched to 90% 1RM (30WM), or 30% 1RM to failure (30FAIL). Exercise at 90RM, 30WM, and 30FAIL differed in total contractions performed (5 ± 0, 14 ± 1 and 23 ± 1, respectively; all P<0.05) and time under tension (16.4 ± 1, 27.1 ± 2, 42.1 ± 1 seconds, respectively; all P<0.05). RESULTS: Mixed MPS was elevated to a greater extent (241%, P<0.05) in the 90RM (0.112 ± 0.020%/hr) compared to 30WM group (0.066 ±.020%/hr) at 4h post-exercise. No difference (P>0.05) was found at 4h between 30FAIL (0.093 ± 0.007%/hr) and 90RM (Figure 1.). The elevation in MPS at 4h post-exercise was greater than 24h (main effect, P<0.05). CONCLUSION: These data suggest that training to maximal failure, independent of training load, induces a greater acute rise in mixed MPS compared to a work-matched control. The greater acute increase in mixed MPS after exercise at 90RM and 30FAIL is likely related to recruitment of more type II muscle fibres not activated in 30WM. These findings support the notion that heavy and light training loads may elicit similar training-induced increases in muscle hypertrophy provided exercise is performed to maximal failure. Supported by NSERC So what does this all mean? In a nutshell the mixed muscle protein synthesis changes were about the same for the 2 failure routines while the worked matched 30% 1RM not to failure was less. Also notice the total time under tension, the 90% 1RM got it done in a lot less time than the 30% 1RM to failure but both produced about the same MPS response. Now the drawbacks of the study. They only compared two intensity extremes 30% vs 90. What would the results have been if they measured 30, 75, 90? Also it doesn't state the training experience of the subjects. So even though it begins to paint a picture of recruitment being a necessity it doesn't quite give all the answers yet, but it is a step in the right direction.