A lack of evidence-based guidelines on how to avoid triggering back pain during sex prompted the research, says co-author Professor Stuart McGill, professor of spine biomechanics at the University of Waterloo, Ontario. The findings are published today in Spine.
"If you survey the primary care physicians around the world, they will tell you that they are absolutely lost when a couple comes to them and says that 'sex causes back pain and in fact we are now abstinent or celibate because we're knackered for two month afterwards'," says McGill.
So McGill and PhD student Natalie Sidorkewicz set out to build an evidence-based and practical 'atlas' matching sexual positions and styles with possible back pain triggers.
They recruited ten healthy couples who were filmed using motion capture and infra-red technology while they had sex. The researchers were in a separate booth where they could hear, but not see, the participants. Electrodes were used to record muscle activity in certain parts of the body to get an idea of force.
Their results showed that existing advice in favour of the 'spooning' position for sex was actually one of the worst positions for individuals with flexion-intolerant back pain—back pain that is worsened by bending over forward or by sitting for long periods of time.
"I'm assuming because people lay on their side, someone thought the spine would be supported and this was good for people, but it turned out not to be true," McGill says. For men with that particular back pain trigger, the study suggested 'doggy-style' sex was far less likely to aggravate the back problem.
In general, the researchers found that the person on top—whether male or female—is most responsible for motion.
For individuals with back pain triggered by movement, the researchers suggested there was no position that would avoid pain, and advised instead that they should try to move more using their hips than their back.
"The more the hinging takes place at their hip, the less the hinging takes place in their spine, the better off [their back is]," McGill says.
Researchers were also able to measure the impact of orgasm on the body, which yielded some surprises. "I had no idea of the range; how it's basically a non-event in some people, through to really substantial muscle contraction in others, and you could see that if they were out of position, they would hurt themselves," says McGill.
The study presented some unique ethical and methodological challenges, not the least being they had to make very discreet inquiries for study subjects from well outside the University community, and ensure that the couple was in a long-term relationship.
They also experienced some interesting technically difficulties; for example, when one couple got accidentally velcroed together by the straps that attached some of the instrumentation.
Having published their data from the male perspective, the researchers are now planning to publish their findings in women, and to look in greater detail at how other factors such as hip replacements or knee replacements might affect individuals.
"We're now targeting very specific sub-categories of back pain, because there's no such thing as non-specific back pain, it's all very specific," McGill says.
From: ABC Science
Grunting in tennis increases ball velocity but not oxygen cost.
Researchers from the University of Nebraska published a study which investigated the effect of grunting in tennis. Ten Division I tennis players (five men, five women) were asked to hit forehand and backhand shots while either grunting or not grunting. Each hitting session consisted of five 2-minute periods with a 1-minute break in between. During the experiment, players wore a portable device that measured metabolic activity while ball velocity was measured with a radar gun. Interestingly, heart rate and oxygen consumption for the two hitting conditions weren't significantly different. But ball velocity was. When players grunted, they hit the ball nearly 4 percent harder. Grunting, researchers discovered, allowed players to hit harder without having to work harder.
“It may be worthwhile for players and coaches in tennis and other sports to experiment with grunting to determine possible improvement in performance,” the researchers said.
Tennis players have been known to judge the spin and speed of the ball, at least in part, by the sound it makes upon striking the strings of their opponent’s racquet. According to Navratilova, a loud grunt at the moment of contact can mask that sound, giving noisy players an edge.
She might be right. In 2010 another study, this time from the University of Hawaii’s psychology department, investigated the impact of grunting on the other player.
Participants in the study were shown videos of a tennis player hitting a ball to either side of a court, sometimes silently, and sometimes with an accompanying sound. As quickly as possible, they had to indicate whether they thought the ball was travelling left or right.
“The presence of an extraneous sound interfered with a participant’s performance, making their responses both slower and less accurate,” the authors said.
“Our data suggest that a grunting player has a competitive edge on the professional tennis tour. The mechanism that underlies this effect is a topic for future investigation.
“For example, the possibility that the interfering auditory stimulus masks the sound of the ball being struck by the racquet or it distracts an opponent’s attention away from the sound of the ball.”
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