Serena Williams has begun training again after a series of health problems including blood clots on her lung. The Wimbledon champion used her Twitter feed to announce her return to the court to her two million followers. Linking to a picture of herself serving in a bright pink body suit, she wrote: "Look who I spotted on the court. Her first day back..." Williams' agent Jill Smoller said the 29-year-old American was "taking it day by day depending on how she's feeling". Former world number one Williams has not played competitively since winning Wimbledon-her 13th Grand Slam title - last July. The American has been unable to compete after cutting her foot on glass in a restaurant when celebrating her triumph at the All England Club. She required two operations on her foot and in February suffered a pulmonary embolism that led to an emergency procedure in Los Angeles. Williams said in March that she was targeting a return to competitive action in "early summer". Source: BBC