Williams raised doubts about coach Chip Kelly's sports science-based practice methods after the Eagles' 37-34 win over the Redskins, in which Williams was beat by Jackson for an 81-yard touchdown in the third quarter.
While many teammates have talked about feeling better than ever before while inseason, Williams said he believes the uptempo practices may be to blame for the Eagles' slow starts.
"I'm just going to be honest with you," Williams said. "It's hard to go out there and fight for 60 minutes when you're fighting throughout the week to make it through one practice. I'm not the only one. I'm just the only one that's man enough to stand up here and talk to y'all. It's obviously, in my opinion, an issue in our starts."
Last week, the Eagles (3-0) came off a Monday night game in Indianapolis. They held a short, low-impact practice late on Tuesday afternoon. They then had their regular sessions Wednesday through Saturday.
Kelly has his players run quite a bit on Saturdays, which is unusual in the NFL.
"When you don't have legs, period, it shows up in games, period," Williams said. "Throughout the game, period."
Kelly disagreed with Williams' assessment during his Monday appearance on Sportsradio 94 WIP in Philadelphia.
"I believe that we're the freshest team in the fourth quarter," said Kelly, who added that the staff monitors each player during practice. "The defense came up huge [at the end]. The way the whole team played in the fourth quarter shows the type of conditioning we have."
Williams said he has had trouble with his hamstrings since last year.
"We've got to start taking care of our guys, taking care of our players," Williams said. "A lot of guys coming in here had no legs. We've got to start taking care of our guys throughout the week in order for us to be productive and have more energy on Sundays. You've got to be smart, as a coaching staff and as players."
The Eagles fell behind 17-0 in their opener against Jacksonville. They were down 17-6 in Indianapolis and 17-7 against Washington.
"Right now, the way we're doing it is not conducive to success," Williams said. "We play several games in practice. It's taxing on your body. I'm 30 years old now. I don't know where I'm going to find that energy. We've been able to fight through that as a team, but some modifications need to be made."