BETHESDA, Md. -- Six months after losing his left leg below the knee to a roadside bomb in Afghanistan, Army Spc. Calvin Todd is smiling, holding his 7-month-old son, Angus ("Gus"), during a break in the Soldier's rehabilitation in Walter Reed National Military Medical Center's Military Advanced Training Center.

"I'm almost back to new," says Todd, 26, who also plays sled hockey and runs eight-minute miles.

Army Staff Sgt. Travis Mills, 26, is one of only five quadruple amputees from the wars in Iraq and Afghanistan to survive his injuries. Critically injured on April 10, 2012 by an improvised explosive device while on patrol during his third tour of duty in Afghanistan, Mills is walking again and able to hold his 18-month-old daughter, Chloe. He also snowboards, swims, water-skis, and rides a bicycle. "Everything you do is adapted," said the Soldier, who describes his life now as "a new normal."

"I'm very fortunate the research that has been done has benefitted me through my injuries," Mills said. "I know that if I would have got hurt like I did 10 years ago, I probably wouldn't have made it off the battlefield," he added.

Since 2001, there have been approximately 1,600 service members that have sustained major limb amputations as a result of the wars in Iraq and Afghanistan; roughly 300 remain on active duty and more than 50 have returned to combat operations, according to Army Capt. Bradley Ritland, chief of the physical therapy amputee section at Walter Reed Bethesda.

Army Col. (Dr.) Chester "Trip" Buckenmaier, head of the Defense and Veterans Center of Integrative Pain Management, said, "war is a catalyst for positive medical change." He added this positive medical change has not only benefitted warriors injured on the battlefield, but society at large, and pointed to first responders at the Boston Marathon explosions, who knew to use tourniquets to help save lives.

More than 260 people were injured after two bombs went off April 15 near the finish of the Boston Marathon, resulting in amputations for at least 14 victims.

Todd and Mills agreed that while those victims face challenges, both emotionally and physically, there is hope. "Stay positive and set attainable goals," Todd said, "the sky's the limit." He aims to compete in a triathlon, and run a road race and a half-marathon or a marathon before the end of the year.

According to Todd, the first couple of months are tough. "It's not going to happen overnight, but you have to work at it. You're still the same person," he said.

Dr. Harold Wain, chief of the psychiatry consultation liaison service at Walter Reed Bethesda, explained all troops returning from deployment in combat zones receive a mental health assessment, and added amputees must learn to accept themselves just as wounded warriors do. "In order for them to have a [positive] recovery, they need to have a good perspective of who they are, they need to feel good about themselves, and they need to accept who they are. They are still whole, and can still function."

David Beachler, lead prosthetist at Walter Reed Bethesda, explained the latest innovation in prosthetics at Walter Reed Bethesda include powered knees, hands and ankles which allow amputees to walk better, run, pick up and grasp objects, type, and perform numerous other daily activities.

"Service members have survived extraordinary blasts injuries and thrived and there's no reason to think the victims of the Boston Marathon explosions will not do the same," said Retired Army colonel, Dr. Paul Pasquina, chair of physical medicine and rehabilitation at Walter Reed Bethesda and the Uniformed Services University.

"We've learned a lot in terms of taking care of individuals who have sustained injuries from a blast," Pasquina said. "Typically from a blast, you have visible wounds and you have invisible wounds, and it's very important to address all of those." This is done by an integrated, interdisciplinary team of surgeons, physicians, nurses, rehab specialists, behavioral health specialists, peer visitors, and the family of the wounded, he added.

Mills said it is just a matter of "continuing to move forward and realizing it will get better."

Todd agreed.

"When you get out of bed and start moving, it's going to come back to you quick, and there's a lot you can do," Todd said. "You can do anything you want to do, you just got to work for it."