John is an athlete runner that has recently changed his diet to vegetarian. he has noticed that despite maintaining their total caloric intake, and training regimen, their lactate threshold has decreased (i. e., they start seeing lactate in their blood sooner). in addition, he tires more easily, and his running times have dropped. after consultation with an expert, john starts eating more lentils, beans and spinach filled with iron. his lactate thresholds go back to normal, as does their athletic performance. what is the complete explanation for john’s decreased lactate threshold and athletic?