Saturday, February 14, 2009

Performance Research for February: Central Fatigue Round 1

That's right, it is Sat early AM and I am up sharing with you the great readers of this blog some very cool research.

More crazy studies once again! Be sure to read my comments below each one and don't let all the uber geek speak scare you away.

Off to conduct some more testing for the Energy Drink study at the U of MN lab. Science "rolls on."

Joint-specific power production and fatigue during maximal cycling.

Martin JC, Brown NA. Department of Exercise and Sport Science, University of Utah, 250 S. 1850 E. Room 241, Salt Lake City, UT 84112-0920, USA.

Cycling power decreases substantially during a maximal cycling trial of just 30s. It is not known whether movement patterns and joint powers produced at each joint decrease to a similar extent or if each joint exhibits an individual fatigue profile. Changes in movement patterns and/or joint powers associated with overall task fatigue could arise from several different mechanisms or from a complex interplay of these mechanisms. The purpose of this investigation was to determine the changes in movement and power at each joint during a fatiguing cycling trial. Thirteen trained cyclists performed a 30s maximal cycling trial on an isokinetic cycle ergometer at 120rpm. Pedal forces and limb kinematics were recorded.

Joint powers were calculated using a sagittal plane inverse dynamics model and averaged for the initial, middle, and final three second intervals of the trial, and normalized to initial values. Relative ankle plantar flexion power was significantly less than all other joint actions at the middle interval (51+/-5% of initial power; p=0.013). Relative ankle plantar flexion power for the final interval (37+/-3%) was significantly less than the relative knee flexion and hip extension power (p=0.010). Relative knee extension power (41+/-5%) was significantly less than relative hip extension power (55+/-4%) during the final three second interval (p=0.045). Knee flexion power (47+/-5%) did not differ from relative hip extension power (p=0.06).

Conclusion: These changes in power were accompanied by a decrease in time spent extending by each joint with fatigue (i.e., decreased duty cycle, p<0.03). style="font-style: italic;">

My notes: When I read the first part of the abstract and the title, I was super excited! Finally some more cool data to look at the effects of joints on overall performance. I have to admit that I was dissapointed in the conclusion, since I think it just made the whole thing more confusing. Perhaps someone other there can help me out.

Frontal and motor cortex oxygenation during maximal exercise in normoxia and hypoxia.

Subudhi AW, Miramon BR, Granger ME, Roach RC. University of Colorado at Colorado Springs.

Reductions in prefrontal oxygenation near maximal exertion may limit exercise performance by impairing executive functions that influence the decision to stop exercising; however, it is unknown if deoxygenation also occurs in motor regions that more directly affect central motor drive. Methods Multichannel near infrared spectroscopy (NIRS) was used to compare changes in prefrontal, premotor and motor cortices during exhaustive exercise. Twenty-three subjects performed two sequential, incremental cycle tests (25 W(.)min(-1) ramp) during acute hypoxia (PIO2 = 79 mmHg) and normoxia (PIO2 = 117 mmHg) in an environmental chamber. Test order was balanced and subjects were blinded to chamber pressure.

Results In normoxia, bilateral prefrontal oxygenation was maintained during low- and moderate- intensity exercise, but dropped 9.0 +/- 10.7 % (mean +/- SD; P < power =" 305"> 0.94). In hypoxia, prefrontal oxygenation was reduced 11.1 +/- 14.3% at rest (P < power =" 256"> 0.61), but deoxygenation was greater in prefrontal than in premotor and motor regions (P < style="font-weight: bold;">

Conclusions: Prefrontal, premotor and motor cortex deoxygenation during high-intensity exercise may contribute to an integrative decision to stop exercise. The accelerated rate of cortical deoxygenation in hypoxia may hasten this effect.

My Notes: I thought this was a very interesting study. The effects of pacing (how hard should I work and at what times to get my best time over a fixed distance) have been proposed for awhile, championed by Dr. Noakes. This provides some evidence that the brain is so smart, that if it is being even slightly deprived from oxygen due to exericse, exercise will stop. Remember, the body is survival orientated, not performance orientated; but we can "back door" performance by increasing survival. This is one of the tennets of Z Health.

Opioid-mediated muscle afferents inhibit central motor drive and limit peripheral muscle fatigue development in humans.

Amann M, Proctor LT, Sebranek JJ, Pegelow DF, Dempsey JA. Institute of Physiology, University of Zürich, Winterthurerstrasse 190, 8057 Zürich, Switzerland.

We investigated the role of somatosensory feedback from locomotor muscles on central motor drive (CMD) and the development of peripheral fatigue during high-intensity endurance exercise. In a double-blind, placebo-controlled design, eight cyclists randomly performed three 5 km time trials: control, interspinous ligament injection of saline (5K(Plac), L3-L4) or intrathecal fentanyl (5K(Fent), L3-L4) to impair cortical projection of opioid-mediated muscle afferents. Peripheral quadriceps fatigue was assessed via changes in force output pre- versus postexercise in response to supramaximal magnetic femoral nerve stimulation (DeltaQ(tw)). The CMD during the time trials was estimated via quadriceps electromyogram (iEMG). Fentanyl had no effect on quadriceps strength.

Impairment of neural feedback from the locomotor muscles increased iEMG during the first 2.5 km of 5K(Fent) versus 5K(Plac) by 12 +/- 3% (P < style="font-weight: bold;">

Conclusion: Our results emphasize the critical role of somatosensory feedback from working muscles on the centrally mediated determination of central motor drive. Attenuated afferent feedback from exercising locomotor muscles results in an overshoot in central motor drive and power output normally chosen by the athlete, thereby causing a greater rate of accumulation of muscle metabolites and excessive development of peripheral muscle fatigue.

My notes: Yep! For optimal performance you need to know what your muscles are doing! Many that I see have some form of SMA--sensory motor amnesia (coined by Thomas Hanna founder of Somatics); they have very poor feedback on what some of their muscle are doing (this seems to almost always correspond to an area with poor mobility). Many times a Z Health mobility drill will be able increase muscle feedback.