Age-related differences in dose response of muscle

Discussion in 'Hypertrophy Research' started by dkm1987, Nov 14, 2008.

  1. dkm1987

    dkm1987 New Member

    Age-related differences in dose response of muscle protein synthesis to resistance exercise in young and old men.Kumar V, Selby A, Rankin D, Patel R, Atherton P, Hildebrandt W, Williams J, Smith K, Seynnes O, Hiscock N, Rennie MJ.
    University of Nottingham, School of Graduate Entry Medicine and Health, Derby, DE22 3DT.

    We investigated how myofibrillar protein synthesis and muscle anabolic signalling were affected by resistance exercise at 20-90% of 1 repetition maximum (1 RM) in two groups of 25 each, postabsorptive, healthy, young (24+/-6 y) and old (70+/-5 y) men with identical body mass indices (24+/-2 kg.m(-2)). We hypothesized that, in response to exercise, anabolic signalling molecule phosphorylation and MPS would be modified in a dose-dependant fashion, but to a lesser extent in older men. Vastus lateralis muscle was sampled before, immediately after, and 1, 2 and 4 h post-exercise. MPS was measured by incorporation of [1,2-(13)C]leucine (gas chromatography-combustion-mass spectrometry using plasma [1,2-(13)C]alpha-ketoisocaparoate as surrogate precursor); the phosphorylation of p70 ribosomal S6 kinase (p70s6K) and eukaryotic initiation factor 4E binding protein 1(4EBP1) was measured using Western analysis with anti-phosphoantibodies. In each group, there was a sigmoidal dose-response relationship between MPS at 1-2 h post-exercise and exercise intensity, which was blunted (P<0.05) in the older men. At all intensities, MPS fell in both groups to near basal values by 2-4 h post-exercise. The phosphorylation of p70s6K and 4EBP1 at 60-90% 1 RM was blunted in older men. At 1 h post-exercise at 60-90% 1 RM, p70s6K phosphorylation predicted the rate of MPS at 1-2 h post-exercise in the young but not in the old. The results suggest that in the postabsorptive state (i) MPS is dose-dependant on intensity rising to a plateau at 60-90% 1 RM; (ii) older men show anabolic resistance of signalling and MPS to resistance exercise.

    A very interesting study with some very interesting results.

    The subjects exercised with their dominant legs at randomly assigned intensities from 20% to 90% 1RM, 5 subjects per group. They performed seated unilateral leg extensions and flexions (1-2 s each) with 2 min rest between sets. They used this tempo to as closely as possible keep the volume of exercise i.e. the force × time-under-tension product (often described as “work”) equal.

    IOW % 1 RM × number of repetitions × number of sets
    so if 1RM was 100lbs
    20%  3 sets × 27 reps = 1620 Arbitrary Work units
    40%, 3 sets × 14 reps = 1680
    60%, 3 sets × 9 reps = 1620
    75%, 3 sets × 8 reps = 1800
    90%, 6 sets × 3 reps. = 1620
    Total work output (i.e.  was 1620 to 1800 units at different exercise intensities, and total time-under-tension was obtained by multiplying by 4 s.)

    Now for the interesting part.

    At intensities up to 60% the response was graded and reflected well with the increases in intensity. Between 60% and 90% of 1RM the response was about equal. Indicating that, in the untrained, myofibrillar PS response is intensity dependant to a point. But once at a point of adeqaute recruitment and activation the response is about equal.

    Some drawbacks or rather areas that could be examined further.

    What would happen if the intensities below 60% were increased in their force/volume, ie more sets taken nearer to failure so recruitement and fiber activation were matched versus just external work? My guess is that PS would be higher than what was seen here.

    What would happen with advanced trainees? Since they used relative intensity I would venture to guess that as the relative RM increases and if novel enough of a stimulus the PS response would still be manifest. (see my earlier posts in this forum)

    What would happen if say they added more work in the higher intensity? Say they added another set in 90% 1RM, would it still equal the 60% 1rm in response magnitude, changing the AUC? My guess is maybe maybe not as it may be a matter of once a threshold in force/volume is hit then doing more would not add any additional benefit.

    Now the other aspect of this study was too compare the difference between young and old. Without great detail or commentary the young showed a significantly higher response but that is nothing new. Yet the old still showed that intensity dependancy correlated.
  2. 9to5lifter

    9to5lifter New Member

    Interesting study, thanks Dan!

    My guess would be that additional sets at intensities below 60% would result in a greater PS response, as you have already indicated.

    The similar results at intensities between 60% and 90% of 1 RM seem to confirm what we already know; after a certain point (threshold) maximal fiber recruitment is achieved. Anecdotal evidence suggests that this is around a person's 8 RM, which seems to be more or less in line with the conclusions of this study.

    What I would really love to know is if additional work (sets) after this "threshold" could elicit a greater response, but I guess we need to wait for other studies. Again, my uneducated guess would be that the response would be slightly higher in this case, but I don't know if this small difference would be worth the effort and the risk (CNS issues, potential tendon problems, motivation etc).

    And yeah, getting old sucks!

    Thanks again,
  3. TunnelRat

    TunnelRat Active Member

    Okay, so what does that mean -- in english...?  [​IMG]
  4. dkm1987

    dkm1987 New Member

    (9to5lifter @ Nov. 20 2008,8:27)</div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">What I would really love to know is if additional work (sets) after this &quot;threshold&quot; could elicit a greater response, but I guess we need to wait for other studies.</div>
    And that's the million dollar question. Bryan states that once the &quot;effective&quot; set is done then additional is only burning calories.

    I tend to agree with that statement as Kennith Baldwin's group showed that the difference between 7 sets and 10 sets was negligible. But that was in rats and looking at specific molecular occurences.

    In light of that what constitutes an effective set? To me and in line with this study it would include a set or a certain number of reps where maximal recruitment and a sufficiently high level of activation is acheived. Which is why I like the premise of using a set number of reps and gauging it with rep speed.
  5. dkm1987

    dkm1987 New Member

    (TunnelRat @ Nov. 20 2008,9:23)</div><div id="QUOTEHEAD">QUOTE</div><div id="QUOTE">Okay, so what does that mean -- in english...?  [​IMG]</div>
    In essence,

    According to this study, using your 10rm or 5rm appears to be irrelevant but if using the lighter side of loading you must do more reps to hit this arbitrary Load/Work threshold.

    So perhaps doing a set of 11 (at your 12RM) then following it up with a set or 2 of 10 or even 8 reps will suffice. This allows sufficient recruitment and the additional sets allow enough fatigue of the initial motor units to kick up activation frequencies.

    Caveat: This study was on untrained people with an acute bout so take it for what it is worth.

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