The first one below is interesting since it points to a more central vs a peripheral effect from training.
When I was a grad student doing my masters in Mechanical Engineering at Michigan Tech (yes, I have been in college FOREVER) I volunteered for a study that involved a microneurography as done in the sudy below. They take a very small needle and stick it directly in the nerve to measure nerve traffic. It was then hooked up to a speaker so that the researcher could hear the nerve impulses to know if he was in the right spot or not.
As he was prodding around in the nerve behind my right knee, I could feel the a sharp shooting pain into my foot or a dull ache around the knee. Very odd.
I used the money from the study to then jump out of a plane (sky diving). I actually did it on a static line so I had to literally crawl out and hang off this pull up bar mounted under the wing of the plane since I had to be a stable position before I let go. Add to this that I am terrified of heights and I was scared out of my skull. I made it, but I took so long to get out to the wing that the pilot had to circle the drop zone again. I am glad I did it, but that was BY FAR the most terrifying experience of my life.
On to the studies!
Resistance exercise training enhances sympathetic nerve activity during fatigue-inducing isometric handgrip trials.
Saito M, Iwase S, Hachiya T.
Applied Physiology Laboratory, Toyota Technological Institute, 2-12 Hisakata Tmpaku-ku, Nagoya, 468-8511, Japan, email@example.com.
Muscle sympathetic nerve activity (MSNA) was investigated 1 week before (pre-training), 1 week after, and 4-6 weeks after strength training using fatigue-inducing handgrip exercises and post-exercise forearm occlusion. Eighteen volunteers underwent forearm training, which consisted of 30 maximal effort, 10-s-duration static handgrips, 4 days per week for 4 weeks. A second group of 18 volunteers served as a control. MSNA was recorded from the tibial nerve by microneurography. Maximal handgrip force increased at 1 week post-training.
The MSNA response during fatigued handgrip also increased at 1 week post-training, as compared to pre-training (52.6 +/- 5.8 vs. 40.6 +/- 4.4 bursts min(-1) (mean +/- SEM), respectively). However, at 4 weeks post-training, MSNA activity returned to the pre-training level (44.0 +/- 5.2 bursts min(-1); p < style="font-weight: bold;">
Conclusion: Our results indicate that an increased muscle sympathetic nerve activity (MSNA) response after strength training is likely to be the result of central neural factors rather than the muscle metaboreflex.
Recurrence quantification analysis of surface electromyographic signal: Sensitivity to potentiation and neuromuscular fatigue.
Morana C, Ramdani S, Perrey S, Varray A.
EA 2991 Motor Efficiency and Deficiency Laboratory, University of Montpellier 1, Faculty of Sport Sciences, 700 Avenue du Pic Saint Loup, 34090 Montpellier, France. This study aimed to assess the capacity of recurrence quantification analysis (RQA) to detect potentiation and to determine the fatigue components to which RQA is sensitive. Fifteen men were divided in two groups [8 endurance-trained athletes (END) and 7 power-trained athletes (POW)]. They performed a 10-min intermittent (5s contraction, 5s rest) knee extension exercise at 50% of their maximal voluntary isometric contraction. Muscular fatigue and potentiation were evaluated with neurostimulation technique. Mechanical (peak torque, Pt) and electrophysiological (M-wave) responses following electrical stimulation of the femoral nerve were measured at rest and every 10s throughout exercise.
Vastus lateralis muscle activity (root mean square, RMS) was recorded during each contraction, and RMS was normalized to M-wave area (RMS/M). During contraction, muscle activity was analyzed with RQA to obtain the percentage of determinism (%Det). At the beginning of exercise, a significant Pt increase (+52%, P<0.001) style="font-weight: bold;">Conclusion: These two results indicated that recurrence quantification analysis detected the peripheral component of fatigue. Conversely, recurrence quantification analysis did not detect central adaptation to fatigue since %Det remained constant when a significant increase in RMS/M (P<0.01)>