Long ago (1970s) - I think it was somebody writing in to Runner’s World magazine - one guy had an approach that was well “out there.” Despite the inherent contradictions in his method, he smoked regularly while training. His theory was that as it compromised his system, he’d end up with more red blood cells as his body tried to supply enough oxygen, much the same effect as training at high altitude. Then he’d not smoke for some time before a race.
