Just browsed through the Abstract. Some unrelated thoughts: I think the issue that most people won't gather up the will to do aerobic exercise after they are mentally exhausted -- even that they know it works to some extent. Following this, I believe, without scientific proof, that genius (or others who can contribute significantly more than other people) have their mind wired completely different from other people.…
Train brazilian jiu jitsu, or another martial art that involves actual physical contact. Mental toughness is a skill that you can develop quickly in endeavors like those.
Generally, pick something that is difficult, or uncomfortable - and do that thing over and over again. It could be as simple a making yourself take 1 minute of cold shower every morning.