We have previously shown that acute exercise increases the level of sphingosine-1-phosphate (S1P) in plasma and ceramide in erythrocytes of untrained subjects. The aim of the current study was to examine the effect of ultramarathon run on the plasma and erythrocyte levels of the following bioactive sphingolipids: S1P, sphinganine-1-phosphate (SA1P), sphingosine, sphinganine, and ceramide. Blood samples were collected from seven male amateur runners participating in a 48-hr ultramarathon race before the run, after 24 and 48 hr of running, and following 24 and 48 hr of recovery. The sphingolipids were quantified by means of HPLC. Sustained running for 48 hr resulted in a progressive decline in plasma S1P to a level significantly lower than at prerace, and then remained stable over the next 48 hr of recovery. In erythrocytes, S1P content was stable until 24 hr of recovery, then rose abruptly to reach peak values after 48 hr of recovery. The plasma level of SA1P decreased progressively during the competition and remained unchanged over the recovery. In erythrocytes, the level of SA1P increased after 24 hr running and normalized thereafter. The level of ceramide, both in plasma and erythrocytes, was not significantly affected by the ultraendurance run. We speculate that reduction in plasma level of S1P during and after the run reduces its biological actions and might be responsible for some negative side-effects of the ultraendurance effort.
Marcin Baranowski, Jan Górski, Barbara Klapcinska, Zbigniew Waskiewicz and Ewa Sadowska-Krepa
Luis Mochizuki, Marcos Duarte, Alberto Carlos Amadio, Vladimir M. Zatsiorsky and Mark L. Latash
We investigated changes in postural sway and its fractions associated with manipulations of the dimensions of the support area. Nine healthy adults stood as quietly as possible, with their eyes open, on a force plate as well as on 5 boards with reduced support area. The center of pressure (COP) trajectory was computed and decomposed into rambling (Rm) and trembling (Tr) trajectories. Sway components were quantified using RMS (root mean square) value, average velocity, and sway area. During standing on the force plate, the RMS was larger for the anterior-posterior (AP) sway components than for the mediolateral (ML) components. During standing on boards with reduced support area, sway increased in both directions. The increase was more pronounced when standing on boards with a smaller support area. Changes in the larger dimension of the support area also affected sway, but not as much as changes in the smaller dimension. ML instability had larger effects on indices of sway compared to AP instability. The average velocity of Rm was larger while the average velocity of Tr was smaller in the AP direction vs. the ML direction. The findings can be interpreted within the hypothesis of an active search function of postural sway. During standing on boards with reduced support area, increased sway may by itself lead to loss of balance. The findings also corroborate the hypothesis of Duarte and Zatsiorsky that Rm and Tr reveal different postural control mechanisms.
Alexander S. Aruin
A number of factors are likely to play a major role in the process of generation of anticipatory postural adjustments (APAs). Among them are the magnitude and direction of an expected perturbation, properties of a voluntary action associated with the perturbation, and features of the postural task such as a body's configuration prior to the action. The aim of this study was to analyze the effect of body configuration on APAs. Experiments were performed on 8 healthy subjects performing fast bilateral shoulder extension movements while standing. Body configuration was modified by instructions to the subjects to stand vertically or with a forward upper body bend varying from 15 to 60°. The electrical activity of postural muscles and displacements of the center of pressure were recorded. Results indicated that APAs were modified with changes in the angular position of the upper body. Decreased anticipatory activation was seen in rectus abdominis and rectus femoris, while increased anticipatory inhibition was observed in erecteor spinae and biceps femoris across conditions with forward bend. As a result, the total anticipatory activity of muscles in a muscle pair in series with a forward bend showed only slight modulation as compared to vertical posture. These results suggest that the CNS uses reorganization of the anticipatory activity of postural muscles by compensating for the changes in APAs of individual muscles in a muscle pair in such a way that the overall anticipatory activity of the muscle pair stays unchanged. Such compensation in counteracting the expected mechanical effects of the perturbation is used to accommodate both changes in the length of postural muscles and diminished stability of the body due to forward bend.
Robert K. Jensen, Tina Treitz and Sylvie Doucet
The purpose of this study was to develop prediction equations to estimate mass, radius to the center of mass (CM), and principal moments of the segments during pregnancy. Nonlinear regression equations were determined for the lower trunk, upper trunk, and thigh. The third sampling month of a longitudinal study was used (Sample 1, n = 15). The nonlinear regressions were then used to predict segment inertias above and below the third sampling month (Sample 2, the remaining 74 measurements). For the remaining segments, body mass and segment lengths were used as predictor variables for mass, radius to CM, and radius of gyration about the centroidal axes. The remaining seven segments did not change substantially during pregnancy, and the means of the repeated measures were used for the simple linear regressions. Eighteen of the 28 regressions and all of the CM regressions were significant. With pregnant subjects it is recommended that these regressions be used if application of the elliptical cylinder model is not possible.
Oleg Verbitsky, Joseph Mizrahi, Arkady Voloshin, July Treiger and Eli Isakov
The goal of this research was to analyze the effects of fatigue on the shock waves generated by foot strike. Twenty-two subjects were instrumented with an externally attached, lightweight accelerometer placed over the tibial tuberosity. The subjects ran on a treadmill for 30 min at a speed near their anaerobic threshold. Fatigue was established when the end-tidal CO2 pressure decreased. The results indicated that approximately half of the subjects reached the fatigue state toward the end of the test. Whenever fatigue occurred, the peak acceleration was found to increase. It was thus concluded that there is a clear association between fatigue and increased heel strike–induced shock waves. These results have a significant implication for the etiology of running injuries, since shock wave attenuation has been previously reported to play an important role in preventing such injuries.
Alex V. Nowicky, Alison H. McGregor and Nick J. Davey
We used transcranial magnetic stimulation (TMS) to study corticospinal excitability to erector Spinae (ES) muscles during graded voluntary contractions in bilateral trunk extension (BTE) and forced expiratory breath holding (FEBH) in normal individuals. Motor evoked potentials (MEPs) could be produced in all subjects in the absence of voluntary activation. At maximum voluntary contraction, levels of surface electromyographic (EMG) activity were 4 times greater during BTE than FEBH. When EMG was normalized to maximum. MEP amplitudes increased in proportion to contraction in both tasks. MEPs in FEBH were compared with extrapolated values at similar EMG levels in BTE and were found to be larger. EMG and MEPs in left and right ES were symmetrical throughout the range of contractions in both tasks. ES muscles have a facilitation pattern similar to that previously shown in leg muscles, but subtle differences at low levels of EMG suggest that the facilitation is dependent on the task.