Friday, September 30, 2011
Wednesday, September 28, 2011
Muscle power attenuation by tendon during energy dissipation
Muscle power attenuation by tendon during energy dissipation
+ Author Affiliations
- ↵*Author for correspondence (nkonow@brown.edu).
Abstract
An important function of skeletal muscle is deceleration via active muscle fascicle lengthening, which dissipates movement energy. The mechanical interplay between muscle contraction and tendon elasticity is critical when muscles produce energy. However, the role of tendon elasticity during muscular energy dissipation remains unknown. We tested the hypothesis that tendon elasticity functions as a mechanical buffer, preventing high (and probably damaging) velocities and powers during active muscle fascicle lengthening. We directly measured lateral gastrocnemius muscle force and length in wild turkeys during controlled landings requiring rapid energy dissipation. Muscle-tendon unit (MTU) strain was measured via video kinematics, independent of muscle fascicle strain (measured via sonomicrometry). We found that rapid MTU lengthening immediately following impact involved little or no muscle fascicle lengthening. Therefore, joint flexion had to be accommodated by tendon stretch. After the early contact period, muscle fascicles lengthened and absorbed energy. This late lengthening occurred after most of the joint flexion, and was thus mainly driven by tendon recoil. Temporary tendon energy storage led to a significant reduction in muscle fascicle lengthening velocity and the rate of energy absorption. We conclude that tendons function as power attenuators that probably protect muscles against damage from rapid and forceful lengthening during energy dissipation.
Wednesday, September 21, 2011
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Friday, September 9, 2011
Thursday, September 8, 2011
From Reuters Health Information
"Eccentric" Exercises May Ward off Hamstring Injuries
By Genevra Pittman
NEW YORK (Reuters Health) Aug 26 - Pro and amateur soccer players who regularly did a particular strengthening exercise were less likely to get sidelined with a hamstring injury, according to a new study from Denmark.
The exercises only take about 10 minutes, and can be done without any extra equipment, researchers said.
Hamstring strains are the most common injury among soccer players, and "it's also the injury that takes out the most days from training and matches," said study author Dr. Per Holmich, from the University of Copenhagen.
The injuries typically happen when players are sprinting and the hamstrings extend to prevent the knee from overstretching. That tension while the muscle is extending is known as eccentric contraction.
It means very high pressure on the muscles, sometimes for long periods of time, Holmich said.
He and his colleagues figured that mimicking that type of pressure in a strengthening exercise might mean the hamstrings were more prepared to deal with high force in practices or matches.
The researchers studied 50 professional and amateur men's soccer teams in Denmark during a full year of practice and play. They trained coaches on half of the teams to lead "eccentric training" exercises during a midseason break and then regularly during the season.
To do the exercises, players pair up, with one athlete on his knees and the other holding the back of the first player's legs and ankles to the ground. The kneeling player slowly leans forward while holding his weight back with his hamstrings, until reaching a push-up position, then pushes himself back up once he hits the ground.
Teams did those exercises up to three times a week during the 10-week break between seasons, then once a week once matches were underway.
Other teams followed their normal training plan with no extra hamstring exercises.
The study involved a total of 942 players. By the end of the year, 67 of them had suffered a hamstring injury -- 15 that did strengthening exercises, and 52 in the training-as-usual group. Athletes that had the strength training were less likely both to get new hamstring injuries and to aggravate a past hamstring injury.
When athletes did get injured, however, there was no difference in how long they were out as a result -- about four weeks in both groups, on average.
Researchers reported online August 8th in the American Journal of Sports Medicine that, based on usual hamstring injury rates, 13 players would have to regularly undergo the strengthening exercises to prevent one injury.
None of the players got injured during the exercises themselves, although they did report muscle soreness after the early sessions.
Previous studies have suggested that this type of training helps players get stronger, but researchers hadn't randomly assigned teams to do or not do the exercises -- so it was less clear that other factors unique to certain teams weren't behind its apparent benefits.
"This is more or less the final evidence that is needed to be sure that this exercise works," said Roald Bahr, one of the researchers who first proposed this type of training, from the Norwegian School of Sport Sciences in Oslo.
Although Holmich and his colleagues only looked at adult male soccer players, the author said there's no reason to think the strengthening exercises wouldn't also help prevent injuries in younger players and in women.
And, he told Reuters Health, "track and field sprinters as well would probably have a good benefit from doing this exercise."
Bryan Heiderscheit, a physical therapist from the University of Wisconsin--Madison, said the exercises showed promise for many different kinds of athletes, including football running backs and wide receivers.
One of the best things about the exercise, Bahr told Reuters Health, is that "you can do this efficiently, with the whole team, on the pitch, without any additional equipment except maybe a towel or some additional knee padding."
"Every soccer team in the world should be doing it."
For further information: http://www.medscape.com/viewarticle/748641?src=mp&spon=8
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