One of the unforgettable images of Patriots training camp came Aug. 5 when the team held a three-hour full-pads joint practice with Washington in hot, humid temperatures, before Bill Belichick capped it off by having players run end-of-practice sprints while imploring them to dig deeper because it could be how they feel in the fourth quarter when a game is on the line. I asked cornerback Darrelle Revis about Belichick’s direct involvement with the team’s conditioning, and he agreed it’s a bit different from what he’s seen in the past, when a strength coach is usually the person leading those drills. Revis shared the viewpoint that it’s not just about conditioning – which will be key with a sweltering season opener Sept. 7 in Miami – but also Belichick’s way of attempting to build mental toughness within his team.