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Alyssa Muething, Shellie Acocello, Kimberly A. Pritchard, Stephen F. Brockmeier, Susan A. Saliba and Joseph M. Hart

Context:

Understanding how muscles activate in a population with a previous glenohumeral-joint (GH) injury may help clinicians understand how to build a conservative treatment plan to strengthen or activate the specific muscles in an attempt to reduce recurrent shoulder injury and development of GH laxity.

Objective:

To investigate muscle-activation differences between the previously injured limb of individuals with a history of GH-joint injury and healthy matched controls during functional isometric contractions.

Design:

Case control.

Setting:

University research laboratory.

Participants:

17 individuals (8 women, 9 men; age 22.3 ± 2.6 y, height 172.4 ± 8.8 cm, mass 75.4 ± 16.5 kg) with previous unilateral shoulder pain and 17 (8 women, 9 men; age 22.9 ± 3.9 y, height 170.9 ± 11.3 cm, mass 73.6 ± 22.9 kg) with no history of shoulder pain or injury.

Intervention(s):

Diagnostic ultrasound measurements of the supraspinatus were completed in both resting and contracted states to assess changes in muscle thickness. Manual muscle tests (anterior deltoid, upper trapezius, infraspinatus, lower trapezius, serratus anterior) and functional isometric contractions (forward flexion, scaption, abduction) were measured using electromyography.

Main Outcome Measures:

Peak, normalized activation of each muscle and supraspinatus thickness activation ratio were compared between groups and bilaterally within groups using separate ANOVAs.

Results:

The anterior deltoid was significantly less activated during all functional isometric tasks in previously injured subjects than in healthy subjects (P = .024). In previously injured subjects, the involved limb-lower trapezius was significantly less activated during scaption and abduction tasks than the contralateral side (P = .022 and P = .031, respectively).

Conclusions:

There were decreases in muscle activation in the anterior deltoid between previously injured and healthy people, as well as in the lower trapezius, in previously injured subjects. Understanding the source of muscle-activation deficits can help clinicians focus rehabilitation exercises on specific muscles.

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Shandi L. Partner, Mark Alan Sutherlin, Shellie Acocello, Susan A. Saliba, Eric M. Magrum and Joe M. Hart

Context:

Individuals with low back pain (LBP) have reduced function of the transversus abdominis (TrA) and lumbar multifidus (LM) muscles. Biofeedback during exercise may increase the ability to contract the TrA and LM muscles compared with exercise alone.

Objective:

To compare TrA preferential activation ratio (PAR) and the percent change in LM-muscle thickness in patients with LBP history before and after exercise with or without biofeedback.

Design:

Controlled laboratory study.

Setting:

University research laboratory.

Patients:

20 LBP individuals, 10 exercise alone and 10 exercise with biofeedback.

Interventions:

Patients were allotted to tabletop exercises in isolation or tabletop exercises with visual, auditory, and tactile biofeedback.

Main Outcome Measures:

TrA PAR and percent change in LM-muscle thickness.

Results:

There were no differences between groups at baseline (all P > .05). Nonparametric statistics showed decreased resting muscle thickness for total lateral abdominal-wall muscles (P = .007) but not TrA (P = .410) or LM (P = .173). Percent TrA thickness increased from table to standing positions before (P = .006) and after exercise (P = .009). TrA PAR increased after exercise (pre 0.01 ± 0.02, post 0.03 ± 0.04, P = .033) for all patients and for exercise with biofeedback (pre 0.02 ± 0.01, post 0.03 ± 0.01, P = .037) but not for exercise alone (pre 0.01 ± 0.02, post 0.02 ± 0.05, P = .241). No group differences were observed for TrA PAR before (exercise 0.01 ± 0.02, exercise with biofeedback 0.02 ± 0.01, P = .290) or after exercise (exercise 0.02 ± 0.05, exercise with biofeedback 0.03 ± 0.01, P = .174). There were no group differences in LM percent change before exercise (P = .999) or after exercise (P = .597). In addition, no changes were observed in LM percent change as a result of exercise among all participants (P = .391) or for each group (exercise P = .508, exercise with biofeedback P = .575).

Conclusion:

TrA PAR increased after a single session of exercises, whereas no thickness changes occurred in LM.