Beckham, 25, posted video footage of his day with trainer Colt Colletti on Thursday.
"Snapchat y'all remember when I was like this here [arm flex emoji], now I'm like this here [two flex emojis]," Beckham wrote on Instagram.
"It's a good lil start."
This is far from the start of Beckham's workout posts. The three-time Pro Bowl selection also posted a video with Colletti in April. During that workout, Beckham sat on a street and used a rope to pull a GMC Yukon Denali toward him. The SUV weighs in at more than 5,400 pounds.
Beckham's Thursday training session included doing a single rep on the bench press with 270 pounds on the bar. Colletti had his hands on the bar the entire time, while serving as Beckham's spotter.
The 5-foot-11, 198-pound wide receiver did seven reps of 225-pounds on the bench press at the 2014 NFL Combine, before becoming the No. 12 overall pick in the 2014 NFL Draft.
Beckham reported to the start of the Giants' offseason workout program in April. He is playing on the final year of his rookie contract. The Giants start OTAs on May 21 and kickoff mandatory minicamp on June 12.