Why Swimming Increases Low Back Degeneration

The newest edition of the Swimming Science Research Review was released on Sunday. 

Background on Swimming and Low Back Degeneration

The shoulder is the primary site of injury in swimmers, but the low back is the second most commonly injured site. In fact, ~8% of those competing at a 2001 International competition experienced low back pain. Despite the anecdotal claims, few studies have compared low back pain and degeneration in swimmers to a control population. Also, comparing specific stroke specialists has also not been performed, limiting the stress from each swimming stroke.

Many feel butterfly and breaststroke are the most problematic strokes to the low back due to the amount of flexion cycles, but this website has already debunked the flexion cycle debate. In fact, rotation actually increases spinal stress, due to the shear stress at the joints.

Research on Low Back Degeneration in Swimmers

Kaneoka (2007) hadfifty-six elite swimmers (M=35, F=21, ~19.6 years) and a control group (38 recreational swimmers; M=24, F=14; ~21.1 years) underwent a magnetic resonance image (MRI). Disc degeneration was compared between groups. Participants also completed a questionnaire about their main strokes as well as their low back pain history.

Thirty-eight (68%) elite swimmers and 11 (29%) controls had degenerated discs at various levels. Disc level L5-S1 was more frequently degenerated in the elite swimming group. However, there was no significant relationship of low back pain symptoms associated with this increase in disc degeneration. Swimmers had a lower rate of low back pain, but back pain was more debilitating.

  
Hangai (2008) analyzed 308 well-trained university athletes (baseball, basketball, kendo, runners, soccer players, and swimmer) and 71 nonathlete university students. Disc degeneration was evaluated with a T2-weighted magnetic resonance image (MRI). A questionnaire concerning low back pain was also performed.

Disc degeneration was significantly higher in baseball players and swimmers compared to the nonathletes. There was an association between low back pain and degeneration and the degree of severity of low back pain with disc degeneration. 

Conclusions on Low Back Degeneration in Swimmers

The L5-S1 segment undergoes greater degeneration in elite swimmers. However, the lack of associating symptoms brings to light the lack of correlation between defects in imaging and symptoms.

Repetitive sports such as baseball and swimming appear to increase incidence of disc degeneration. These sports also have greater rotation than the others studied, one possible mechanism of degeneration.Disc degeneration is a higher risk in swimmers compared to nonathletes, yet injury rate was not significantly higher in swimmers. It seems low back pain and degeneration do not correlate, at least in the acute term. Longer studies must assess the degree of degeneration and injury rate later in life. Nonetheless, it seems swimmers have greater degeneration, but not injury rate. Moreover, swimmers and coaches should not be alarmed if an athlete undergoes an MRI and sees degeneration, as degeneration is greater in asymptomatic swimmers.

Reference

1. Kaneoka K, Shimizu K, Hangai M, Okuwaki T, Mamizuka N, Sakane M, Ochiai N. Lumbar intervertebral disk degeneration in elite competitive swimmers: a case control study. Am J Sports Med. 2007 Aug;35(8):1341-5. Epub 2007 Apr 3.
2. Hangai M, Kaneoka K, Hinotsu S, Shimizu K, Okubo Y, Miyakawa S, Mukai N, Sakane M, Ochiai N. Lumbar intervertebral disk degeneration in athletes. Am J Sports Med. 2009 Jan;37(1):149-55. doi: 10.1177/0363546508323252. Epub 2008 Sep 17.