At this year's Teacherathalon, Ms. Frizzle squares off with Mr. Sinew (Dan Marino), a muscle-bound gym teacher. Sinew easily wins the first of the three events. Thinking there's a problem, the kids go inside Ms. Frizzle to check her out. The bus takes them through her lungs to the bloodstream, where they get pumped through her heart to her calf muscle. But when Frizzle's leg muscle collapses from the strain of winning the second event, the kids discover that her red blood cells can't get oxygen to her muscles fast enough! Can the kids help Frizzle recover in time to win the final race?
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