| Summary: | Thesis (MSc)--University of Stellenbosch, 2001. === ENGLISH ABSTRACT: A 5 km cycling time trial (TT) demands high, sustained muscle power output and
substantial oxidative and glycolytic energy delivery. The aims of this study were to firstly
use the novel approach of using Peak Sustained Power Output (PSPO) as a predictor of
cycling performance for variable fixed-workload testing and 5 km time trialing and
whether oral creatine supplementation would affect 5 km time trial performance and
metabolism. The effect of oral creatine supplementation with 20 g/day for 7 days on 5 km
time trial performance and metabolism after a random-variable workload protocol
(stochastic test) was investigated in a single-blind placebo controlled study. Thirteen
trained male cyclists volunteered for the study that was approved by the University of
Stellenbosch Research Ethics Committee. We hypothesized that Cr supplementation
would affect time trial performance as well as the appearance of breakdown products of
adenine nucleotides in the plasma. Baseline: the subjects' peak power output was
measured and they underwent a baseline stochastic test followed immediately by a 5 km
time trial (STI) and on a different day, a single 5 km time trial test (Tl) was undertaken.
Study 1: In the following week the subjects repeated the stochastic test with 5 km time
trial (ST2) and on a different day a 5 km time trial (T2). During T2 blood samples were
taken at regular intervals as well as during recovery. A muscle biopsy was taken after T2
in the recovered state. The major performance predictors were the 5-km time trials (TTl
and TT2) with a coefficient of variation between the thirteen trained male cyclists of
0.6%. The 5 km time trials in the fatigued state (STI and ST2) had a coefficient of
variation of 0.7%. Results: There was a significant difference between 5 km TT
performed fresh and 5km TT performed fatigued (P=0.0001). The decrement in time
ranged between 1.0 sec to 38.0 sec. The relationship between two different high intensity
endurance performance tests: PSPO and 5 km TT (TT mean) had a correlation ofr=-0.79
P<O.OI. The correlation between PSPO and the 5 km TT performed in the fatigued
condition (ST mean) was r= -0.60 P<0.05. There was also a relationship between age and
PSPO (F 0.73; P<0.05). Age showed a good negative relationship with TT mean (F-
0.71; P<0.05). Mass and PSPO were also correlated (FO.85; P<O.OI). Plasma lactate
concentrations were significantly different from rest at all other time points P<O.OOOIup
to 20 minutes post-exercise. Hypoxanthine (P<O.OOOI)and urate (P=O.05) concentrations were also significantly different from rest at all other time points. There was a significant
change in plasma hypoxanthine concentrations over time (P<0.0001). There was a
significant correlation between plasma lactate concentration at time 0 in recovery and %
Myosin Heavy Chain (MHC) I (FO.59, P<0.05) and % MHC na (F -0.61, P<0.05). Area
under the curve for hypoxanthine showed significant relationships of F -0.53 (P=O.05)
and F 0.56 (P<0.05) respectively for %MHC I and %MHC ITa. Study 2 -
Supplementation: following T2 the subjects received Cr or placebo powder containing
sachets to be ingested 4 times daily for the next week with carbohydrate also provided.
Post-supplementation testing: the subjects returned and conducted another variable fixedworkload
test with 5 km time trial (ST3) as well as a single 5 km time trial (T3). They
once again underwent the same blood sampling routine and had another muscle biopsy in
the rested state. The average of ST1 and ST2 was used as the major measure for
performance under fatigued conditions and TTmean. Results: there was a significant
difference between 5 km TT performed fresh and 5 km TT performed fatigued
(P=0.0001). Plasma lactate, hypoxanthine and urate samples were taken at the postloading
5 km time trial (TT3). The levels of these plasma metabolites were compared to
the concentrations of those sampled at TT2 and between the creatine and placebo groups.
The plasma hypoxanthine levels were significantly different from rest for both the
creatine and placebo groups (P<0.0001). Plasma urate had significant change in
concentrations over the time points (P<0.005). Another significant difference was found
between the creatine and placebo groups for the pre-and post tests conducted (P<0.005).
The creatine group showed a non-significant increase (7%) in mean total intramuscular
creatine concentration. No significant differences were found in the mean values for total
nucleotide concentration pre- and post loading in the creatine and placebo groups.
Conclusions: The 5 km performance test resulted in high values for plasma lactate,
hypoxanthine and urate, an indication of fatigue induced by this performance test. Oral
creatine supplementation did not improve performance significantly in the variable fixedworkload
protocol 5 km time trials or the individual 5-km time trials and had an effect on
adenine nucleotide metabolism in both the variable fixed-workload protocol 5-km time
trial and individual 5 km time trial performance tests. === AFRIKAANSE OPSOMMING: Die 5 km fietsry tyd toets (TT) verg hoëvolgehoue, spierkrag en wesenlike oksidatiewe
en glikolitiese energie verskaffing. Die doelwitte van hierdie tesis was eerstens om 'n
nuwe fietsergometer toets te ontwerp vir die voorspelling van kompetisie prestasie. Die
toets was 'n veranderlike, voorafvasgestelde werkladingstoets (VVWT). Dit is vergelyk
met 'n maksimale volgehoue kraguitsetingstoets (MVKT) en 'n 5 km TT. Daarna is
bepaal ofkreatien supplementasie 'n effek sou hê op enige van hierdie oefeningstoetse of
metabolisme tydens die 5 km TT. Die supplementasie eksperiment was 'n enkelblinde,
plasebo-gekontroleerde studie ontwerp. Dertien manlike fietsryers het vrywilliglik
deelgeneem. Resultate: Daar was 'n statisties betekenisvolle verskil tussen die 5 km TT
wat vars onderneem is en die wat direk na die VVWT onderneem is (P=O.OOOl). Daar
was ook 'n betekenisvolle korrelasie tussen die twee verskillende hoë intensiteit korttydsvak
oefeningstoetse (r=-0.79 P<O.Ol vir TT en MVKT). Plasma laktaat konsentrasies
was betekenisvol verhoog met vergelyking van die monsters geneem tydens rus en all
ander onteledings tydspunte (P<0.0001) tot en met 20 minute na oefening. Hypoxantien
(P<O.OOOl) en uraat (P=0.05) konsentrasies was ook betekenisvol verskillend van rus by
alle ander tysdpunte. Daar was 'n betekenisvolle korrelasie tussen plasma laktaat direk na
oefening en die % Myosien Swaarketting (MIlC) I (r=0.59, P<0.05) en % MHC ITa (r= -
0.61, P<0.05). Studie 2 - Na supplementasie was daar geen verskil in oefeningsprestasie
nie maar wel in plasma metaboliet waardes van nie. Gevolgtrekkings: Die 5 km TT het
baie hoë waardes vir plasma laktaat tot gevolg gehad, asook hypoxantien en uraat, 'n
indikasie van die hoë mate van vermoeienis deur hierdie oefeningtoets berwerkstellig.
Kreatine supplementasie kon nie oefeningsprestasie verbeter nie.
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