Shoulder extension strength: a potential risk factor for shoulder pain in young swimmers?
The shoulder is the most frequent site of pain and time loss injury in swimmers, In all cohorts, shoulder pain prevalence in swimmers is high, increasing with time in the sport and may range from 40 to 91% depending on the age group and definition. The quest for risk factors include range of shoulder rotation movement, shoulder muscle strength, shoulder muscle imbalance, flexibility, scapular kinematics, core stability, use of equipment,training load, swimming technique, dry land exercise and breathing side but none have conclusively been causative and as such injury prevention strategies are difficult to justify when evidence regarding shoulder strength, remains inconclusive, but this may be function specific.
Shoulder Internal and external rotation strength and their ratios have commonly been reported in swimmers, with changes in these values suggested as risk factors for shoulder pain but shoulder flexion(FL) and extension (EX) strength values have rarely been reported and warrant further investigation, given the high propulsive forces generated by the swimmer in shoulder elevation and the ensuing challenge to the stabilising muscles of the shoulder.
This study measures Isometric shoulder strength values for IR, ER, FL and EX, bilaterally using a hand-held dynamometer for 85 young ( 14-20) swimmers with no shoulder pain . Tests were performed in supine for shoulder FL and EX (in 140◦abduction); and IR and ER (in 90◦abduction). The swimmers were then followed for 24 months and a questionannire consisting of seven questions to determine if shoulder pain had developed and if so: which shoulder was affected; an estimation of the swimming sessions modified or missed due to shoulder pain; training history; and if the swimmer had stopped swimming, reasons why this was the case.
Thirty-seven swimmers (47%) returned completed questionnaires and eighteen (n = 27 shoulders) of these swimmers reported the development of shoulder pain. The average time for follow up was 18 months (range 9–24 months). Swimmers who reported pain had asimilar estimated weekly training time to those that did not report pain (mean [SD] 10.3 ± _6.6 and 10.9 ± _6.3 h, respectively) and mean age (16.3 ± _2.1 and 16.4 ± _1.8 years, respectively). There was no relationship between a historical episode of shoulder pain (prior to strength testing) and the development of shoulder pain in this group of swimmers for any strength values (p > 0.20).
In male swimmers, EX strength was lower in shoulders which had developed pain (median 12.35% BM; range 7.06–28.06; p = 0.04)compared to those with no reported experience of shoulder pain(16.55% BM; 9.51–21.30; p = 0.04) with no difference in FL strength between these groups (p = 0.16). The FL:EX strength ratio was higher for the shoulders with pain.
In female swimmers there were no significant differences in shoulder muscle strength values (FL, EX, ER, IR) ratios (IR:ER and FL:EX) between the shoulders that developed pain and those that did not (p ≥ _0.05)
The results of this study suggest that shoulder EX strength and consequently FL:EX strength ratio have a significant relationship with the development of shoulder pain in young male swimmers The male swimmers who developed shoulder pain were weaker in relative shoulder EX (12.35% BM) than those males who did not develop shoulder pain (16.55% BM; p = 0.04),
Shoulder EX strength was not associated with the development of shoulder pain in females swimmers which may reflect different developmental stages of strength gain throughout adolescenece.
The authors recommend monitoring young male swimmers with shoulder EX less than 13.5% BM as they may be at risk of developing shoulder pain.