His project's title was "Community sport participation and provision", and the fellowship enabled him to visit the United States and West Germany.

In 1969 he represented Great Britain's senior open team in Hamburg, West Germany, winning the 400-metres aged 17 years four months.

He went on to compete for Great Britain in the 1972 Summer Olympics held in Munich, Germany in the 4 x 400-metre relay where he won the silver medal with his teammates Martin Reynolds, Alan Pascoe and David Hemery.

Commentating on the race for the BBC David Coleman remarked that Jenkins had the "greatest run of his life", when he won the 4 × 400 m relay.

[12] Both David and his brother Roger feature prominently in the book A Life In A Day In A Year[13] by Peter Hoffmann which describes their athletics training at Meadowbank Sports Centre, Edinburgh and their racing careers between 1973 and 1978.

[14] Scottish documentary company, Pelicula Films, featured David Jenkins during his training in 1975 as he prepared for the 1976 Olympic Games (Montreal, Quebec, CA).

In 1978 he won a gold medal competing for Scotland at the Commonwealth Games in Edmonton, Canada in the 4 × 100 m relay, alongside Cameron Sharp, Allan Wells and Drew McMaster.

"[19] In January 1986 Jenkins met with Juan Javier Macklis, who owned Laboratorios Milanos, a pharmaceutical plant in Tijuana, Mexico, that was contracted to supply medicines for the Mexican government.

In April 1987, weeks before federal prosecutors filed the indictment, Jenkins was arrested and later entered a guilty plea for the trafficking of steroids worth approximately $100 million through the Tijuana border crossing.

It was reported that at one time Jenkins and co-conspirators Dan Duchaine and William Dillon were responsible for up to 70% of the steroids trafficked in the United States.

[8] Jenkins was sentenced by Judge J. Lawrence Irving in US District Court San Diego to seven years in the Boron Federal Prison Camp in California's Mojave Desert.

[19] Referring to David Hemery, the gold medal winner of the 400 metres hurdles at the 1968 Summer Olympics in Mexico City, Jenkins told The Independent that "I sold him down the river, and that wasn't cool."

In addition, in the late 1970s he met with and visited Paul Fireman, head of a US sporting goods distributor, in Boston introducing him to Reebok and helping establish the then embryonic brand in the United States.

[24] In 1988, Jenkins started his nutrition company and began working on a protein powder, convinced that its muscle-building properties could be marketed as a healthy, legal alternative to steroids.

In 1993 he set up a partnership with Dan Duchaine, a well known steroid guru and two-time convicted felon, and founded Next Proteins, a company which produced dietary supplements for athletes and bodybuilders.