If you think old age means a slow slip into fragility, think again.

Gladys Ngwenya, 77 years old. | Cosmo City, South Africa | (REUTERS/Siphiwe Sibeko)

In South Africa's Cosmo City, just outside Johannesburg, a group of about 30 women, ages 60 and above, gear up twice a week in sparring gloves and step into the ring for boxing lessons. The goal is to keep their bodies active and healthy while also learning how to defend themselves.

"If somebody tries to attack me, I will punch him, really. Really, I will hit him badly," 67-year-old boxer Mable Makhosi told the BBC. Makhosi said her weekly boxing regimen has lowered her blood pressure and improved her conditions as a diabetic.

Constance Ngubane, 79 years old. | (REUTERS/Siphiwe Sibeko)

(REUTERS/Siphiwe Sibeko)

Former bodybuilder Claude Maphosa founded the boxing program for senior women about four years ago and now works as their coach. "I've never trained somebody that old," he told the BBC. "I've always thought they're fragile, only to realize that there's more to them, and there's more to what they wanted to do. So I gave them the opportunity, and they ended up training me instead of me training them because their energy level was just too high."

Research shows exercise improves muscle strength and slows bone density loss in older people. It can also lead to a cornucopia of positive health benefits for the elderly, from reducing the risk of cardiovascular disease, type-2 diabetes, and some forms of cancer, to mitigating the effects of anxiety and depression.

"I like boxing. Whenever I train, I feel younger. I don't get pains. I feel good," said 75-year-old Zodwa Twala. "I'll never quit."

Below, check out these tough grannies as they duke it out and defy expectations of what elderly people can do.

(REUTERS/Siphiwe Sibeko)

(REUTERS/Siphiwe Sibeko)

(REUTERS/Siphiwe Sibeko)

Mable Makhosi, 65 years old. | (REUTERS/Siphiwe Sibeko)

(REUTERS/Siphiwe Sibeko)

Zodwa Thwala, 70 years old. | (REUTERS/Siphiwe Sibeko)

(REUTERS/Siphiwe Sibeko)

Constance Ngubane, 79 years old. | (REUTERS/Siphiwe Sibeko)