On Monday, the Kansas City Chiefs players returned to the University of Kansas Hospital Training Complex for the beginning of Phase One of the offseason workout program.

For those who don't already know, Phase One consists of lifting, conditioning and physical rehabilitation only.

It's an important time for the players to get a baseline of strength, conditioning and flexibility heading into the 2015 NFL season.

During this two-week period, the strength and conditioning staff members are the only ones who can work with the players.

Barry Rubin, the head strength and conditioning coach for the Kansas City Chiefs, put it simply.

"Our season started on Monday," he said.

After a couple days of workouts, Rubin is comfortable with what he's seen from the players.

"I'm very happy with them," Rubin said. "You can tell that most of them have been working. We had like 15 guys that were coming in (during the offseason) and they did a great job. But you could tell as a whole, they're ready to go.

"I'm very pleased after a couple of days."

The commitment by the players coming to the offseason workouts in a good spot physically should be expected of a team looking to build upon the franchise's first back-to-back winning seasons in almost a decade.

Leading this charge right now is Rubin, who enters his 19th year as a NFL strength and conditioning coach and his third in Kansas City.

After spending five years with the Philadelphia Eagles (2008-12), Rubin joined Andy Reid in Kansas City before the 2013 season. Before that, Rubin spent 11 years with the Green Bay Packers (1995-05).

Even with all that experience, Rubin is always learning, adapting and looking for new ways to improve his craft.

"We like to do something different every year, even if it's just small tweaks," Rubin explained. "Coach (Reid) allows me to go out to some strength and conditioning specialists after the season and learn some things and bring those techniques back here."

As the players made sure to get their bodies right heading into the start of this offseason program, Rubin explained how they ramp up the workouts throughout the offseason.

"It's a progression," he explained. "We'll start with higher volume and lower intensity and as the offseason progresses, the volume drops but the intensity rises.

"We do a lot of stabilization; that's a mainstay. We do some kind of stabilization work every day."

Rubin continued.

"We center our program on squats, bench press and some form of Olympic lifting—power cleans. "That's kind of your bread and butter as far as getting you strong and explosive."

On Thursday, the offensive players worked out in the morning while the defensive guys went in the afternoon.

The players will train with their specific positional group, as Rubin caters the workouts to different athletic needs and techniques.

"We want it to be specific for their position," Rubin explained. "The linemen pushing the sled while the skill guys pulling it.

"They all do the short acceleration sprints to improve on their speed and they all do some kind of plyometric drills to help with their explosiveness."

Besides quarterbacks and receivers, who can work on routes and timing as long as there aren't any defenders present, the rest of the players aren't able to do any football-related workouts on the field.

But within the scope of what they're allowed to do right now, Rubin likes what he's seen from the players.

This has also been the first opportunity for a few of the new players to integrate with their new teammates.

Guys like Jeremy Maclin, Tyvon Branch, Ben Grubbs and Paul Fanaika are meeting many of their new teammates for the first time, something Rubin enjoys seeing.

"So far it's been really good, we've got a great bunch of guys here," Rubin explained of getting everyone together. "It's not a cliquish team, it's not a bunch of selfish guys. Besides really good athletes and football players, they're really good people."

Phase One of the offseason program lasts for two weeks, and then Phase Two will begin. Phase Two lasts for three weeks and includes individual positional work and "perfect play" drills, but no offense versus defense.