Posterior shoulder tightness is a common cause of shoulder impingement syndrome, labral lesions, and rotator cuff tears in clinical rehabilitation and sport activities (Ludewig and Cook, 2002; Tyler et al., 2000; Wilk et al., 2002; 2005). Posterior shoulder tightness is often assessed by measuring the range of motion (ROM) of glenohumeral internal rotation (IR) and horizontal adduction (HA) (Bach and Goldberg, 2006; McClure et al., 2007). A restricted ROM of IR and HA is caused by tightness of posterior muscles (i.e., infraspinatus and posterior deltoid) and the posterior capsule (Borsa et al., 2005; Poser and Casonato, 2008; Yang et al., 2012). Passive cross-body stretch is an effective method for stretching these areas (McClure et al., 2007).
Short-term (3- to 8-week) stretching program increases ROM by changing mechanical properties, such as increasing the length of stretched muscle, inducing elongating connective tissue, and increasing the number of sarcomeres in series (McNair et al., 2001; Taylor et al., 1995; Reid and McNair, 2004). However, although ROM increases after single stretching session, increased muscle length is transient and some studies have demonstrated that muscle stiffness (passive torque/ angle curve) do not change significantly (Law et al., 2009; Ben and Harvey, 2010; BjArklund et al., 2001). Increased muscle extensibility after stretching is due to sensory modification, rather than increased muscle length, an idea referred to as sensory theory (Nelson and Bandy, 2004; Weppler and Magnusson, 2010). Namely, stretching can increase the stretch tolerance at the terminal position of the stretch, resulting in increased muscle extensibility and ROM (Folpp et al., 2006; de Weijer et al., 2003; Weppler and Magnusson, 2010).
A previous study speculated that local cryotherapy (LC) may help endure the uncomfortable stretch sensation, felt at the final position of the stretch (Brodowicz et al., 1996). Stretching the hamstring with ice on it more effectively improved supine hamstring flexibility than both stretching alone and stretching with heat (Brodowicz et al., 1996). In addition, whole body cryotherapy effectively increases the active ROM of glenohumeral flexion, abduction, external rotation, and IR in patients with adhesive shoulder capsulitis (Ma et al., 2013).
To date, no studies have investigated the effects of LC on posterior shoulder muscles for the improvement of ROM of IR and HA, through modification of the stretch sensation at the end range of passive IR and HA. Thus, in this study, we investigated the effects of LC on the stretch sensation and on the ROM of glenohumeral IR and HA, comparing it to passive cross-body stretch and no stretching. We also investigated the lasting effects of LC and stretching (separately) at a 10-min follow-up assessment. We hypothesized that LC would decrease the uncomfortable stretch sensation, resulting in an increased ROM of IR and HA and have a lasting effect, similar to stretching.
We recruited 87 subjects with posterior shoulder tightness selected from students of Yonsei University, Korea (Table 1). Using previously published immediately changes in posterior shoulder tightness (Moore et al., 2011), a power of 80% and an a level of 0.05 were assumed and the difference of the glenohumeral IR ROM should be at least 4.2[degrees] between the three groups, which required at least 25 subjects were needed. The inclusion criteria for selection of healthy subjects with posterior shoulder tightness was a difference in the passive ROM of the glenohumeral IR of over 10[degrees] between the right and left side (between-side difference; mean [+ or -] standard deviation [SD], 16.93 [+ or -] 10.81) (McClure et al., 2007). We excluded subjects who had present or previous shoulder pain, history of shoulder surgery, reduced sensation, Raynaud's disease, previous cold allergies or who were unable to perform glenohumeral active IR and HA. Random-number generator function in Microsoft Excel program automatically and randomly matched 87 subjects to each group: the LC group (29 subjects), the stretching group (29 subjects), and the control group (29 subjects). Then subjects were provided the allocation information. Before the study, the principal investigator explained all procedures to the subjects in detail and gave subjects one week to make a decision on participating this study. All subjects signed an informed consent form, and this study was approved by the Yonsei University Wonju Institutional Review Board.
Glenohumeral active and passive ROM of IR and HA, stretch sensation, and pressure pain threshold (PPT) were measured at pre-intervention, post-intervention (immediately after intervention), and 10-min follow-up (10 min after the post-intervention period) by a single tester who was blinded to the random group allocation.
Measurement of posterior shoulder tightness
Measurement of posterior shoulder tightness included active and passive IR and HA using a gravity inclinometer (Acuangle, Isomed, USA). Prior to ROM measurements, subjects were asked to perform three bilateral shoulder flexion exercises with hands clasped, holding at the end of range for 10 s as a warm-up (McClure et al., 2007). Shoulder flexion exercise was used as warm-up to minimize the extensibility effect on posterior structures and IR and HA, and warm-up exercise was able to ensure subject's safety and to facilitate the consistency of data being tested (Kolber and Hanney, 2010). The subjects were positioned in the resting supine position. To measure active ROM of IR, a subject's arm was placed in glenohumeral abduction at 90[degrees] on a therapeutic table and elbow flexed at 90[degrees] without glenohumeral IR or ER. A tester's hand was placed on the anterior region of the subject's glenohumeral joint and the other hand was used to place an inclinometer on the distal, posterior part of the forearm. Subjects were asked to perform glenohumeral IR until the tester felt an upward movement of the anterior region of the glenohumeral joint. The tester recorded the value in degrees. ROM for passive IR was measured in the same position and a tester performed passive IR until the tester felt an upward movement of the anterior region of the glenohumeral joint (McClure et al., 2007). The tester recorded the value in degrees. Active and passive IR measurements were repeated three times with 30 s of rest between each trial and the mean value was used for data analysis.
To measure the active glenohumeral HA ROM, subjects assumed a supine position with the glenohumeral joint at 90[degrees] of abduction...