TY - JOUR

T1 - Effects of experimental muscle pain on shoulder-abduction force steadiness and muscle activity in healthy subjects

AU - Bandholm, Thomas Quaade

AU - Rasmussen, Lars

AU - Aagaard, Per

AU - Diederichsen, Louise

AU - Jensen, Bente Rona

N1 - CURIS 2008 5200 010

PY - 2007

Y1 - 2007

N2 - We previously demonstrated that the steadiness of shoulder abduction is reduced in patients with subacromial impingement syndrome (SIS), which might be related to shoulder pain associated with the SIS. The aim of the present study was to examine the acute effects of experimental shoulder muscle pain on shoulder motor function in healthy subjects. The fluctuations in exerted force (force steadiness) and electromyographic (EMG) activity from eight shoulder muscles were determined during sub-maximal isometric and dynamic contractions with the shoulder abductors in nine healthy subjects (27.7 +/- 4.2 years, mean +/- 1 SD) before, during and after experimental pain induction. Experimental pain was induced by bolus injections of 6% hypertonic saline into the supraspinatus muscle. Experimental muscle pain reduced shoulder-abduction force steadiness on average by 21% during isometric contractions (P = 0.012) and tended to do so during concentric contractions (P = 0.083). Middle deltoid, and infraspinatus and lower trapezius muscle activity increased (3-5% EMG(max)) during isometric and concentric contractions, respectively (P < 0.05). Thus, experimental shoulder muscle pain reduced the steadiness of isometric shoulder abduction and caused small changes in the abduction activation strategy. The observed effects of experimental pain on shoulder motor function differed from that observed previously in patients with SIS and chronic pain during the same types of contractions. A possible explanation may be that, even though the adopted experimental pain-paradigm may reflect the SIS in terms of the painful structures, it might not reflect the adaptations in the central nervous system seen with chronic pain.

AB - We previously demonstrated that the steadiness of shoulder abduction is reduced in patients with subacromial impingement syndrome (SIS), which might be related to shoulder pain associated with the SIS. The aim of the present study was to examine the acute effects of experimental shoulder muscle pain on shoulder motor function in healthy subjects. The fluctuations in exerted force (force steadiness) and electromyographic (EMG) activity from eight shoulder muscles were determined during sub-maximal isometric and dynamic contractions with the shoulder abductors in nine healthy subjects (27.7 +/- 4.2 years, mean +/- 1 SD) before, during and after experimental pain induction. Experimental pain was induced by bolus injections of 6% hypertonic saline into the supraspinatus muscle. Experimental muscle pain reduced shoulder-abduction force steadiness on average by 21% during isometric contractions (P = 0.012) and tended to do so during concentric contractions (P = 0.083). Middle deltoid, and infraspinatus and lower trapezius muscle activity increased (3-5% EMG(max)) during isometric and concentric contractions, respectively (P < 0.05). Thus, experimental shoulder muscle pain reduced the steadiness of isometric shoulder abduction and caused small changes in the abduction activation strategy. The observed effects of experimental pain on shoulder motor function differed from that observed previously in patients with SIS and chronic pain during the same types of contractions. A possible explanation may be that, even though the adopted experimental pain-paradigm may reflect the SIS in terms of the painful structures, it might not reflect the adaptations in the central nervous system seen with chronic pain.

U2 - 10.1007/s00421-007-0642-1

DO - 10.1007/s00421-007-0642-1

M3 - Journal article

C2 - 18066578

VL - 102

SP - 643

EP - 650

JO - European Journal of Applied Physiology

JF - European Journal of Applied Physiology

SN - 1439-6319

IS - 6

ER -