Thesis (MSc (Physiological Sciences))--University of Stellenbosch, 2006. / Despite a growing interest into the mechanisms of the repeated bout effect, little is known about the
consequences of chronic eccentrically biased training and the possible advantageous such training may offer
to athletes as well as patients with muscle-debilitating disease. This study investigated the role of satellite
cells in the muscle adaptation in response to either downhill or uphill high intensity training (HIT). Welltrained
endurance runners were divided into two training groups matched for training volume and 10 km
running times (n = 6, uphill training, UP; n = 6, downhill training, DH) and subjects in both groups
completed 10 HIT sessions over a period of 4 weeks. Running performance was tested before and after the
training intervention by a 10 km road race and peak treadmill speed (PTS) in horizontal and inclined (+5%)
laboratory incremental tests to exhaustion. Skeletal muscle biopsies were sampled at baseline, after 2 HIT
sessions, and after 4 weeks of HIT. Muscle was analysed immunohistochemically for satellite cell frequency
as identified by CD56 and M-cadherin (Mcad) expression. Myogenin protein contents of muscle homogenates
were determined by western blotting. Myosin heavy chain (MyHC) isoform proportions and mean fibre crosssectional
area was measured. During the HIT intervention, UP exercised at a higher percentage of their HRmax
than DH (mean ± SD, 97 ± 1 vs. 92 ± 3 %HRmax, p < 0.005), but at a similar rate of perceived exertion (RPE).
DH completed more intervals per session and covered greater distance per session than their UP
counterparts. Both training groups increased their training intensity but decreased their training volume
during the 4 weeks of HIT. The combined group of 12 athletes improved their PTSgradient (mean ± SD, 16.7 ±
0.8 vs. 17.3 ± 1.0 km/h, p < 0.05). No significant differences between groups were found for PTS, VO2max or
10 km performance. Satellite cell frequency in this cohort of trained runners (48.9 ± 10.3 km/week) at
baseline was similar to healthy young males (CD56+ cells/fibre, 0.19 ± 0.10). Satellite cell frequency
increased significantly in DH after 4 weeks (Mcad, 123%; CD56, 138%) and non-significantly in UP (Mcad,
45%, CD56, 39%). No significant differences were found after two training sessions or at any time between
groups. Mcad and CD56 expression correlated well (r = 0.95, p < 0.0001). Muscle myogenin content
increased for both groups (UP: 56%; DH: 60%) after 4 weeks. No notable changes were seen after two training
sessions. However, myogenin levels 2 days after session 1 correlated well (r= 0.99, p<0.005) with muscle pain
experienced on the same day, as measured by the visual analogue scale. No changes were seen in the MyHC
proportions or the fibre cross-sectional area after the training intervention. It was concluded that the training
intervention was too short to induce changes in MyHC distribution or fibre area. Is seems likely that satellite
cell proliferation was initiated as an early response to DOMS, but the response was maintained for 4 weeks.
However, due to the lack of change in fibre morphology and myonuclear number, the role of satellite cell
proliferation in fibre type transformation or muscle hypertrophy could not be established. Similarly, various
possible roles for increased myogenin protein are offered, but since the origin of myogenin expression
(satellite cells vs. myonuclei) was not determined, no definite conclusion regarding the precise function can
be made. In conclusion, this study is the first to definitively indicate satellite cell proliferation in well-trained
endurance runners in response to a change in training, including specifically downhill HIT. This response
was early and sustained. This study asks several questions about the role of satellite cells during muscle
adaptation to repetitive downhill training, and lays a foundation for further research into this unexplored
field.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2218 |
| Date | 03 1900 |
| Creators | Eksteen, Gabriel Johannes |
| Contributors | Myburgh, K. H., University of Stellenbosch. Faculty of Science. Dept. of Physiological Sciences. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1367160 bytes, application/pdf |
| Rights | University of Stellenbosch |
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