Madonna's unsightly vein bulges out after hardcore workout with Gwyneth Paltrow

The star emerged from yet another workout with a bizarre zig-zag vein throbbing from her temple, a sign she may be taking her punishing workouts too far.

The Queen of Fitness is famous for enduring two-hour sessions six days a week, and strenuous exercise is known to increase the blood flow which makes veins bigger.

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And today it appears she's worked out extra hard, spurred on by the presence of her best pal turned training buddy Gwyneth Paltrow.

The actress, who has just returned from a visit to New York, joined health fanatic Madonna on a morning workout at the pop star's £6million personal gym, which is just 20 yards from her front door.

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They were also joined by Madonna's pint-sized personal trainer and constant gym companion Tracy Anderson, who is no stranger to the Hollywood mother of two.

It was, after all, Gwyneth who found her first.

After giving birth to baby Moses in 2006, the health-conscious actress was confronted with a weight gain of more than 2 1/2st.

Following a strict diet, the star managed to shift half of it within several weeks, but that last stone proved to be impossible; and for months she resorted to wearing two Spanx girdles at a time.

With the start date for her film, Iron Man, fast approaching, Gwyneth made a last-ditch attempt to get her body into shape, and called on Tracy.

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The 35-year-old noticed results immediately and now appears, even after two children, to have the best body she's ever had.

Tracy has now been working with Madonna, who turns 50 in August, six days a week for the past year.

Madonna and Gwyneth share more than just a desire to be in great shape - earlier this year Gwyneth apparently began exploring Kabbalah, the branch of Jewish mysticism the singer follows.

Gwyneth, who last week denied her marriage to Coldplay star Chris Martin is in trouble, was spotted leaving a New York Kabbalah Centre earlier this year.

A source told Mail Online at the time: "She's a seeker, and with Madonna's encouragement, she's now looking into Kabballah - she's simply on a personal quest."