Short-term effects of bracing on exercise performance in mild idiopathic thoracic scoliosis

In adolescent idiopathic thoracic scoliosis (ITS) working capacity may be reduced during exercise. Despite concern about its usefulness, bracing is still being used in ITS. Thus the effects of bracing on exercise performance need to be examined. We studied six females, ages 12-15 years who had mild ITS (Cobb angle range 20-35 degrees). Pulmonary volumes, maximal voluntary ventilation (MVV), breathing pattern, the lowest (most negative in sign) pleural pressure during sniff maneuver (Pplsn), and pleural pressure swings (Pplsw) were measured first. Then, Pplsw, O2 uptake (VO2), CO2 output (VCO2), heart rate (HR) at rest and during progressive incremental exercise on a cycling ergometer (10 watts/min) were recorded. The exercise test was performed under control conditions without bracing (C) and after 7 days of bracing with the braced on (B). Dyspnea was measured by a modified Borg scale. At rest, bracing mildly affected total lung capacity and forced vital capacity (p < 0.03 for both) but not breathing pattern, Pplsn, or Pplsw (%Pplsn), a measure of respiratory effort. Furthermore, bracing did not consistently affect maximum work rate (WRmax). In both B and C VO2 was below (< 70%) the predicted value, VE was below (< 45%) MVV, and HR reserve was < 15 beats/min, indicating some cardiovascular deconditioning. On the other hand, respiratory frequency (Rf) increased more in B than in C (p < 0.03). In addition, Pplsw, Pplsw (%Pplsn), and Pplsw (%Pplsn)/VT, an index of neuroventilatory dissociation (NVD) of the respiratory pump, were greater in B (p < 0.03 for all). At a similar work rate, the Borg rating score was greater with bracing on than off, and the difference (delta Borg) tended to relate to concurrent changes in Pplsw (%Pplsn)/VT (r2 = 0.71; p < 0.07). We conclude that bracing affects respiratory effort, NVD, and dyspnea score during progressive exercise. These effects are consistent with increased lung elastance. Diminished exercise tolerance in patients with mild ITS probably reflects impaired physical fitness but is not affected by bracing. Training programs proposed for this subset of patients to increase peripheral muscle performance might also consider NVD of the respiratory pump.