Australia's out-door track season starts too early -- curse of geography and latitude. In order to be ready for the late summer Euro competitions and global championships, they have to take a late spring break or run the starch out of themselves. The proof is that their peak performances "usually" take place down under.
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Speaking of young phenom's:
I don't put much stock in young early bloomers. Future potential is -- usually -- happening right "then and there." Potential is a concept too often loaded with the emotional baggage of wishful thinking. If a -- for example -- short legged, quick starting, fast accelerating specimen has finished growing and has good running technique and form; then there's not too much more you can squeeze out of him other than speed endurance and PED's (e.g. Shirvo 10.03-19 yrs. old). The synapses, twitch fibers, lever-lengths are all genetically fixed at that point. Sounds very pessimistic, I know, but consider the history of most -- "Wonder boys & girls" -- and the realism smacks the wishful thinking out of your optimism (forums are overflowing with would've-could've-should've laments). Anecdotally one can point to reasons (or excuses) for ones particular pet cause not fulfilling the upward performance trend of that "growing years" graph, and forums are such repositories. In general though, it's the case that they had reached their full potential, we just wanted more (There are the counter-exception small samples as well for the anecdotally inclined to latch onto).
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There have only been two Caucasian short-sprints athletes -- since Dave Sime -- who REALLY have had the (((top-end speed))) to excite me -- Lemaitre & Guliyev. The rest, have been just quick-squat-spark-plugs, made for futbol, or beneficiaries (good not great e.g. "Borzov") of amateurism or just beginning shamateurism (when the sport was not a practical long-term endeavor for those living in non-communist nations) therefore less competition than would have been otherwise.
I don't include Wells and Mennea; both had decent top-end speed in a relatively slow era just beginning to attract pros. They overlapped the amateur/pro transition but appear to have been juicers. The ridiculous growth of Mennea's jaw finally made sense when he admitted after retirement his use of HGH. This "confession" occurred when HGH was added to the PED list. He conveniently claimed his HGH use (legal at the time since it wasn't on the doping radar) was post-Moscow/1983(?)-1988 (1977-1980 his peak years after stagnating in 1976 Olympics). Wells sudden Charles Atlas bod, from pre-25yrs. old skinny geek and sudden burst of speed (10.15 in 1978 after just barely running under 11.00 in 1976 age 24 for the first time) are typical of "born again" cheaters. The accusations coming from those who trained with him I suspect are true.
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Ps......The real comparison of speed between the races is when you compare NASA spacecraft Helios-1 & 2 traveling at a speed of 70 km/ps or 150,000 mph compared to the African spear. My retired greyhound can outrun Bolt, so why are we so worried about our simian cousins being "perhaps" (take a deep breath) faster. Evolutionarily speaking, the Negro on occasion still needs to run from lions in the mudderland, and in Civilization they are regularly running from the Po-po. Feets don't let me down, whereas we, when we feel the need for speed, hop in our supersonic fighter jets and pull G's.