Turnig to the grain of truth this description might provide, as I noted in my earlier essay on Spartan appearance, Spartans were apparently generally taller than their contemporaies, which is probably the result of more meat in their diet. Since one of the most striking differences about the rearing of girls in Sparta compared to treatment of female infants and children elsewhere is Greece was that they received the same food as their brothers, this meat-heavy diet would have been fed Spartan girls too. Yet elsewhere in Greece, girls and women were fed a different, "simpler" diet with no "extras," (to use Xenophon's words) than their brothers. In short, the difference in height between Spartans and the citizens from other cities would have been even more extreme when comparing women to women than men to men.
In addition, Spartan girls were expected to run and even race -- hence Aristophanes' reference to Lampito's "easy stride." Indeed, if we are to believe Xenophon and Plutarch, Spartan girls were taught wrestling, and were expected to master the bow and javelin, and certainly to master horses -- all things that might make a comedian compare them to women capable of "strangling a bull."
Certainly, Spartan girls could run, swim and dance. They took part in races both on foot and driving chariots, and they took part in public dances. All this entailed spending a good deal of time outside in the fresh air, and that meant that Spartan girls were exposed to the elements and their skin would have tanned the Greek sun. It also meant that they grew up getting a great deal of excercise -- probably more than most girls get today, and they would very likely have been sleek and lean like their brothers, at least while growing up and in the agoge. After all, Xenophon and Plutarch stress that the girls were being treated like their brothers that regime produced the tall, lean youth of the agoge.
Girls in other Greek cities were, in contrast, not allowed to set foot outside their houses and were expected to be "sedentary." So while the Spartan girls grew tall and fit, women in the rest of Greece grew up stunted from a diet short on protein, rarely had access to fresh air, and did not exercise. The impact on physical appearance of other Greek women would have been women significantly shorter than their own men (much less Spartans) and without muscles -- though not necessarily thin. (A girl who eats too much of a carbohydrate-intensive diet and does not move more than a few feet in the course of a day can still grow fat, but she is not likely to be lean much less strong.) In short, the contrast between the physical appearance of Spartan and other Greek girls and maidens would have been much more striking than between Spartan and other Greek boys and men.
Admittedly, after marriage Spartan women, unlike their husbands, were no longer compelled to exercise or to eat at common messes, so they might have become comparatively soft and fat. However, they still had responsibility for their households and this entailed considerable amounts of outside work and exposure to fresh air and sunlight so that it seems unlikely that Spartan women competely lost their physical condition. Furthermore, because Spartan women did not marry until their late teens/early twenties, they would have been brought to childbed at the optimal age, while girls in other Greek cities generally married much younger and bore their first child at 15 or 16, with all the known negative consequences for their health.
Finally, I would like to suggest that Spartan women's education, literacy and economic power also had an impact on their appearance. Women who are raised to think they are important to their society, who are literate and encouraged to voice their opinions, women who have real power tend to stand straighter, hold their head high and move with confidence. I find it hard to image Spartan women sitting hunched over with bowed heads as the women of Athenian pottery do.
In conclusion, Spartan women would generally have been taller than other women, more physically fit, tanned, and over time they would have aged better -- indeed the very probably had a much longer life expectancy than women elsewhere in Greece! In addition, they would have held themselves with self-assurance and moved with greater confidence. Perhaps the combination of these things would indeed have made them seem strong (and brave) enough to "strangle a bull" when compared to their contemporaries.