"Well, I hit the weights really hard over the past couple of months," Mathews said. "I was lifting really hard with James Lark and all my best lifts were this semester. I exploded in all my lifts and have never done as good as I did."
Mathews has added around 20 pounds of muscles to his 6-foot-4-inch frame. He's gone from around 205 pounds to nearly 230 pounds of muscle mass.
"I feel bigger, I feel stronger and I feel better. I'm in the best shape of my life right now."
Despite the added weight, Mathews has apparently not lost any speed.
"When we did our times and stuff, all of my times were just as fast or faster than last year when I weighed 20 pounds less," he said. "I feel really good and I feel faster."
Mathews played in all 13 games last season and started in three. As a flex tight end, he caught 27 passes for 299 yards and one touchdown.
When he was a high school recruit, the knock on Mathews was his lack of athleticism due to a lack of flexibility.
"I really worked on my flexibility and my stretching," said Mathews. "I just did what they say and worked hard on it and I feel good."
Mathews' quest for physical development and athletic refinement came by way of some constructive criticism from his position coach.
"I went and talked to Coach Reynolds and he told me things I needed to work on," Mathews said. "He talked about my weaknesses and he said it was my fluidity and my flexibility. You know what I mean? Being able to be fluid in my routes and not so robotic and stiff."
At the wide receiver position, younger brother Mitch Mathews looked very good on Monday, especially having not played the game in two years. His speed and athleticism getting off the line of scrimmage was visibly noticeable, along with his 6-foot-6-inch frame. Marcus worked out with his younger brother to develop that fluidity and flexibility Coach Reynolds wanted.
"My brother Mitch came back from his mission and he's that way," said the older Mathews. "He's really fluid and flexible and is going to be an All-American wide receiver one day. I have no doubt about that.
"We were talking about something yesterday, and that was nobody will outwork us. So I was watching how he plays because we're two different type of players. He's super fluid and shaky and I'm more straight-line, so we're trying to take things from each other's game. It's really helped me a lot being with my brother and learning to be more fluid and be more flexible."
In the one-on-one drills and skeli drills, Marcus consistently was seen beating his defender over the top. Time and time again, he was running downfield with a defender in pursuit.
"Yeah, I had a really good day for my first day of spring camp," Mathews said. "I just think I've gotten faster even though I've added more weight. I feel really good and I feel more fluid and more agile downfield. I think a lot of it comes from that."
Not only did Mathews practice and play at the y-receiver or flex-tight end position, he also expanded his role at the tight end position on the first day of spring camp.
"There's going to be a transition with me at the tight end spot with me doing more blocking," Mathews said. "[Monday] was a really good practice for me I thought. I'm not exactly where I need to be but I had a really good first day of spring practice. I'm trying to be more that three-point tight end [attached to the line of scrimmage] along with being that flex tight end."
The three-point or attached tight end requires more size for blocking, which Mathews has added. It also requires a different mindset as well.
"It's a different mentality and different mindset," he said. "You have to also adjust how your routes go, and you have to have a mindset of a blocker. Out there when you're flexed you don't get touched as much. When you're down there on the line of scrimmage you now have to go put your head into someone's face and just smash. It's something that you have to get used to. You have to go from being a fluid, finesse tight end at the flexed-y position to putting your head down and just mashing mentality and pushing your guy back."
The more diverse role at the tight end position was something Mathews wanted to add to his skill set.
"I wanted to be that guy," Mathews said. "I was tired of just being that one-dimensional flexed tight end, you know. I didn't want to be that guy. I wanted to be that all-around guy and didn't want to come out when a certain formation was called. I wanted to be that all-around guy that could be out there for any situation. That's why I've worked so hard to put on weight and develop certain aspects of my athleticism to be the best I can and help the team."