'No Pain, No Gain' Applies to Strength Training



SAN DIEGO – Induced knee pain appears to have improved strength training in a small, Danish randomized trial.

Researchers injected the right knee infrapatellar fat pads of 13 healthy subjects in their mid-20s with painful, hypertonic saline. Immediately afterward, participants did three sets of leg presses and knee extensions. After three sessions per week for 8 weeks, their right quadriceps were 22% stronger than at baseline. Fourteen controls, injected with nonpainful isotonic saline, increased quadricep strength by 7% (P less than .0001).

The results suggest "maybe it’s not that bad to exercise with pain, at least if it’s not caused by inflammation."

Common wisdom holds that pain diminishes muscle function, inhibits strength training, and may prevent rehabilitation in patients with knee problems, including osteoarthritis. However, "no one has ever proven that is actually the case," said Tina Sorensen, a doctoral candidate at the Institute of Sports Science and Clinical Biomechanics at the University of Southern Denmark in Odense, a physiotherapist who was lead author.

The results suggest "maybe it’s not that bad to exercise with pain, at least if it’s not caused by inflammation"; perhaps they also hint at a role for induced pain in some settings, she said. The researchers are interested now in seeing if their early results hold up in patients with actual knee problems.

Loads used in training were 80% of a given subject’s maximum repetition strength, which was assessed weekly and without pain. Participants worked each set to the point of muscle fatigue, usually 8-12 repetitions, and rested about a minute between sets.

The groups were evenly matched, with no significant differences in height, body mass index, or baseline strength. There were 10 men in the pain group and 6 in the control group, but as with other factors, the difference was not statistically significant.

The injections (1 mL of saline under ultrasound guidance) came after a 10-minute warm-up on a stationary bicycle. The pain from the hypertonic shots diminished as subjects worked through their sets, starting on average at about 25 mm on the 100 mm visual analog pain scale and ending at about 10 mm. Strength was assessed weekly 30 minutes after training.

At the end of the 8 weeks, the right legs of participants in the pain group were 24.6% stronger at 60 degrees of knee extension, 21.6% stronger at 120 degrees, and 19.6% at 180 degrees. Subjects in the control group were 7.5% stronger at 60 degrees of knee extension, 5.0% at 120 degrees and 8.2% at 180 degrees.

"It could be that when you have pain, your type 1 muscle fibers [the endurance fibers,] are inhibited, and your type 2 fibers [the power and speed fibers] are easily recruited, which could explain why the pain group had the larger increase in muscle strength," Ms. Sorensen said at the World Congress on Osteoarthritis, which was sponsored by the Osteoarthritis Research Society International.

The researchers noted that hypertonic saline injections mimic many aspects of pathological knee pain "and [are] a well-accepted, efficient, and safe method to" replicate it experimentally.

The work was supported by the Association of Danish Physiotherapists. Ms. Sorensen said she has no disclosures.

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