Over the weekend, many fitness enthusiasts take advantage of their extra free time to go on long bike rides, epic runs and other all-day fitness extravaganzas. But if you've only got half an hour, a new study shows that's all you need to get the weight loss benefits of exercise.

Sixty "moderately overweight" Danish men participated in a study at the University of Copenhagen. They all wished to lose weight and committed to regular exercise for three months. They either biked, rowed or jogged for either 30 or 60 minutes. Researchers found that, all else controlled for, the men who exercised for 30 minutes lost an average eight pounds, while the 60-minute men lost only six pounds on average.

Why? The researchers guess that the hour-long workout prompted a compensatory rise in appetite that negated the extra work. Or, perhaps, the longer workout left participants more exhausted, diminishing their activity levels for the rest of the day.

In any case, it's happy news that a 30 minute workout is all it takes, so here are some suggestions for a quick weekend jaunt:

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  • Canoe For 2 Miles

    You can burn 315 calories in 30 minutes of canoeing at the vigorous but <a href="http://www.healthstatus.com/cgi-bin/calc/calculator.cgi" target="_hplink">manageable pace of four miles per hour</a>.

  • Bike 6 Or 7 Miles

    In 30 minutes, <a href="http://www.healthstatus.com/cgi-bin/calc/calculator.cgi" target="_hplink">you can burn just</a> under 300 calories by cycling at a moderate clip.

  • Spend Half An Hour On The Basketball Court

    Just 30 minutes of playing full-court ball <a href="http://www.healthstatus.com/cgi-bin/calc/calculator.cgi" target="_hplink">will burn 373 calories</a>.

  • Run 3 Miles

    Lacing up and running a 10-minute mile, you can burn 342 calories <a href="http://www.healthstatus.com/cgi-bin/calc/calculator.cgi" target="_hplink">in a three-mile loop</a>.

  • Walk 2 Miles

    Walking at a brisk pace for just two miles can burn 175 calories -- and help you see your neighborhood in a new way.

  • Swim 60 laps

    At a <a href="http://www.everydayhealth.com/Calories-Burned-Swimming.htm" target="_hplink">slow pace of 50 yards per minute</a>, you can cover 1,500 yards in a half-hour -- or 60 laps in a standard, 25-yard pool. <em><strong>CORRECTION</strong>: The original version of this slide erroneously identified the number of laps at 300. We regret the error.</em>

  • Rollerblade For 6 Miles

    Burn 357 calories in 30 minutes by rollerblading a six mile loop at the <a href="http://www.lenihan.org/sk8_calories.htm" target="_hplink">moderate pace of 12 miles per hour</a>.