Submitted on March 26, 2008
Revised on September 30, 2008
Accepted on October 12, 2008
Short-term immobilization and recovery affect skeletal muscle but not collagen tissue turnover in humans
Britt Christensen1, Eva Dyrberg1, Per Aagaard2, Michael Kjaer3, and Henning Langberg1*
1 Institute of Sports Medicine and University of Copenhagen
2 University of Southern Denmark
3 Bispebjerg Hospital and Faculty of Health Sciences, University of Copenhagen
* To whom correspondence should be addressed. E-mail: hl02{at}bbh.hosp.dk.
Not much is known about the effects of immobilization and subsequent recovery on tendon connective tissue. In the present study, healthy young men had their nondominant leg immobilized for a 2-week period followed by a recovery period of the same length. Immobilization resulted in a mean decrease of 6% (5413 to 5077 mm2) in CSA of the triceps surae muscles and a mean decrease of 9% (261 to 238 Nm) in strength of the immobilized calf muscles. Two weeks of recovery resulted in a 6% increased in CSA (to 5367 mm2), whereas strength remained suppressed (240 Nm). No difference in Achilles tendon CSA was detected between the two legs at any time-point. Local tendon collagen synthesis, measured as the peritendinous concentrations of PINP (indirect marker for collagen synthesis), was unchanged after 2 weeks of immobilization. However, peritendinous levels of PINP were significantly elevated in the immobilized leg (15 to 139 ng/ml) following 2 weeks of remobilization when compared to preimmobilization levels. In contradiction hereto, systemic concentrations of PINP remained unchanged throughout the study. Immobilization reduced muscle size and strength, while tendon size and collagen turnover was unchanged. While recovery resulted in an increase in muscle size, strength was unchanged. No significant difference in tendon size could be detected between the two legs after 2 weeks of recovery, although collagen synthesis was increased in the previously immobilized leg. Thus, 2 weeks of immobilization are sufficient to induce significant changes in muscle tissue, whereas tendon tissue seems to be more resistant to short-term immobilization.
