Kinesiology

Improving Shoulder Kinematics in Individuals With Paraplegia: Comparison Across Circuit Resistance Training Exercises and Modifications in Hand Position Linda M. Riek, Joshua Tome, Paula M. Ludewig, Deborah A. Nawoczenski

Background. Circuit resistance training (CRT) should promote favorable kinematics (scapular posterior tilt, upward rotation, glenohumeral or scapular external rotation) to protect the shoulder from mechanical impingement following paraplegia. Understanding kinematics during CRT may provide a biomechanical rationale for exercise positions and exercise selec- tion promoting healthy shoulders.

Objective. The purposes of this study were: (1) to determine whether altering hand position during CRT favorably modifies glenohumeral and scapular kinematics and (2) to compare 3-dimensional glenohumeral and scapular kinematics during CRT exercises.

Hypotheses. The hypotheses that were tested were: (1) modified versus traditional hand positions during exercises improve kinematics over comparable humerothoracic elevation angles, and (2) the downward press demonstrates the least favorable kinematics.

Design. This was a cross-sectional observational study.

Methods. The participants were 18 individuals (14 men, 4 women; 25–76 years of age) with paraplegia. An electromagnetic tracking system acquired 3-dimensional position and orientation data from the trunk, scapula, and humerus during overhead press, chest press, overhead pulldown, row, and downward press exercises. Participants performed exercises in traditional and modified hand positions. Descriptive statistics and 2-way repeated-measures analysis of variance were used to evaluate the effect of modifications and exercises on kinematics.

Results. The modified position improved kinematics for downward press (glenohumeral external rotation increased 4.5° [P�.016; 95% CI�0.7, 8.3] and scapular external rotation increased 4.4° [P�.001; 95% CI�2.5, 6.3]), row (scapular upward rotation increased 4.6° [P�.001; 95% CI�2.3, 6.9]), and overhead pulldown (glenohumeral external rotation increased 18.2° [P�.001, 95% CI�16, 21.4]). The traditional position improved kinematics for overhead press (glenohumeral external rotation increased 9.1° [P�.001; 95% CI�4.1, 14.1], and scapular external rotation increased 5.5° [P�.004; 95% CI�1.8, 9.2]). No difference existed between chest press positions. Downward press (traditional or modified) demon- strated the least favorable kinematics.

Limitations. It is unknown whether faulty kinematics causes impingement or whether pre-existing impingement causes altered kinematics. Three-dimensional modeling is needed to verify whether “favorable” kinematics increase the subacromial space.

Conclusions. Hand position alters kinematics during CRT and should be selected to emphasize healthy shoulder mechanics.

L.M. Riek, DPT, PhD, Department of Physical Therapy, Nazareth Col- lege, 4245 East Ave, Rochester, NY 14618 (USA). Address all corre- spondence to Dr Riek at: [email protected].

J. Tome, MS, Department of Phys- ical Therapy, Ithaca College, Ithaca, New York.

P.M. Ludewig, PT, PhD, Depart- ment of Physical Medicine and Rehabilitation, Programs in Physi- cal Therapy and Rehabilitation Science, University of Minnesota, Minneapolis, Minnesota.

D.A. Nawoczenski, PT, PhD, Department of Orthopaedics, Uni- versity of Rochester Medical Cen- ter, Rochester, New York.

[Riek LM, Tome J, Ludewig PM, Nawoczenski DA. Improving shoulder kinematics in individuals with paraplegia: comparison across circuit resistance training exercises and modifications in hand position. Phys Ther. 2016; 96:1006 –1017.]

© 2016 American Physical Therapy Association

Published Ahead of Print: December 4, 2015

Accepted: November 22, 2015 Submitted: January 5, 2015

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Spinal cord injury (SCI) is the sec-ond most common cause of paral-ysis in the United States, with a prevalence exceeding 1.3 million peo- ple.1 Of those people with SCI, approx- imately 45% are classified as having para- plegia.2 Relying heavily on their upper extremities for functional independence, up to 67% of people with paraplegia report having existing shoulder pain.3–5

Chronic shoulder pain following SCI is consistently reported during activities of daily living, including transfers,3,4,6 –11

wheelchair propulsion and manage- ment,3,4,7,10,12,13 and lifting objects from overhead.3,4,7,10,12 Due to the risk of developing shoulder pain following para- plegia and its impact on functional inde- pendence, maintenance of shoulder health and prevention of shoulder pain are essential.

The majority (�70%) of shoulder pain is diagnosed as mechanical impinge- ment.6,13,14 Impingement can be catego- rized as either subacromial (external) or internal based on the structures that are compressed or mechanically irritat- ed.15–18 Subacromial impingement occurs at lower ranges of humerotho- racic elevation (45°– 60°) and affects structures that pass between the cora- coacromial arch and the humeral head18

(Fig. 1A). Subacromial impingement is a contributor to rotator cuff tendinopathy development in people with SCI, as wheelchair users frequently function in lower ranges of humerothoracic eleva- tion during functional tasks including transfers and wheelchair propulsion. Conversely, internal impingement occurs at higher ranges of humerotho- racic elevation (above 105°) and affects the articular surface of structures that pass between the glenoid fossa and humeral head16,17,19 (Fig. 1B). Beyond approximately 90 degrees of arm eleva- tion,20,21 internal impingement is more likely occurring than subacromial impingement. Internal impingement is also a likely contributor to rotator cuff tendinopathy development in people with SCI, as wheelchair users frequently function in higher ranges of humerotho- racic elevation during functional tasks including reaching activities. Because individuals with SCI have the need to function at both lower and higher ranges

of humerothoracic elevation, mechanical impingement (subacromial or internal) is believed to be a primary mechanism in the development of rotator cuff disease, which can progressively result in rotator cuff tears.22,23

To date, shoulder kinematics, a poten- tially important etiologic factor for shoul- der impingement, has primarily been described during exercise or functional activities in the able-bodied popula- tion.24 –31 A study by Nawoczenski et al32

in individuals with SCI and impingement, however, demonstrated potentially detri- mental glenohumeral and scapular kine- matics during weight-bearing tasks including transfers. For instance, findings include nearly 6 degrees of increased scapular anterior tilt on the trailing arm for the group with shoulder pain versus the group without shoulder pain during the lift-pivot phase of a transfer.32 As opposed to a preventive measure, exer- cise traditionally has been used following SCI as an intervention to treat shoulder impingement after it occurs.7,12,33

Circuit resistance training (CRT) is one form of exercise that also is recom- mended across the rehabilitation spec- trum to facilitate independent function- ing with the upper extremities (Appendix). Despite the evidence to sup- port physiological benefits of CRT exer- cise,34 –38 few studies in the able-bodied population or SCI literature have ana- lyzed or verified which exercises to select based on kinematic rationale for minimizing mechanical impingement risk. Furthermore, it also is unknown whether modifications to the exercises via changes in hand position can favor- ably influence kinematics during CRT. A recent study that investigated shoulder kinematics during execution of CRT demonstrated that certain exercises pose more mechanical impingement risk than others.39 Exercises were rank ordered from highest to lowest subacromial mechanical impingement risk (down- ward press, horizontal row, chest press, overhead pulldown, and overhead press) and internal mechanical impingement risk (overhead press and overhead pull- down) based on collective kinematic and exposure data.39

Recommended upper extremity exercise programs ideally should promote the most favorable scapular or glenohumeral kinematics (scapular posterior tilt, upward rotation, or external rotation or glenohumeral or external rotation)24 –31

during the exercise regimen to maximize the subacromial space40 and protect the shoulder from mechanical impingement. A more comprehensive understanding of the kinematics that occur during CRT at specific humerothoracic elevation ranges, linked to impingement risk, may provide guidance on which exercises to emphasize, modify, or eliminate with regard to maintaining a healthy shoulder.

The purposes of this study were: (1) to determine whether glenohumeral and scapular kinematics can be favorably modified during wheelchair-based CRT exercises by altering hand position and (2) to compare 3-dimensional (3D) glenohumeral and scapular kinematics during CRT exercises prescribed for indi- viduals with paraplegia. We hypothe- sized that modified hand positions dur- ing 5 CRT exercises (overhead press, chest press, overhead pulldown, hori- zontal row, and downward press), as opposed to traditional hand positions, would result in more favorable scapular and glenohumeral kinematics (scapular posterior tilt, upward rotation, or exter- nal rotation or glenohumeral external rotation) when averaged over compara- ble humerothoracic elevation angles. We also hypothesized that during the 5 CRT exercises (traditional or modified posi- tion), the downward press would dem- onstrate the least favorable kinematics. The ultimate goal was to develop specific recommendations regarding exercise positions and selection of specific exer- cises for CRT that emphasize healthy shoulder mechanics.

Method Study Design We used a pure within-subject design with factors being hand position (2 lev- els) and exercise (5 levels for the lower range of humerothoracic elevation and 2 levels for the upper range of humerotho- racic elevation).

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Participants Participants were part of a broader study39 and were recruited from the community as a sample of convenience. Twenty individuals (15 men, 5 women), ranging in age from 25 to 76 years, with paraplegia and minimal to no shoulder pain met the inclusion and exclusion cri- teria. Inclusion criteria were: greater than 1 year after SCI; SCI from trauma or of vascular or orthopedic origin, with an injury at the second thoracic level or below; and requiring a manual wheel- chair for primary mobility. Exclusion cri- teria were trauma, dislocation or surgery of the glenohumeral or acromioclavicu- lar joints, shoulder pain (pain �10 on the Wheelchair User’s Shoulder Pain Index), and positive impingement tests (includ- ing Hawkins, Neer, resisted external rota- tion, and painful arc) that may alter or prevent completion of exercise testing. All data collection and testing were con- ducted at a local community fitness center. Prior to participation in the study, all participants provided university-approved informed consent.

Exercise Protocol Participants were seen for 2 sessions. During the first session, participants underwent a clinical evaluation that included a musculoskeletal evaluation and the completion of the Wheelchair User’s Shoulder Pain Index to ensure inclusion and exclusion criteria were met. The primary purpose of the initial session was to establish the 1-repetition maximum (1RM) that would be used dur- ing the subsequent session. The Mayhew regression equation41 was used to calcu- late the 1RM for each CRT exercise (overhead press, chest press, overhead pulldown, horizontal row, and down- ward press) and was calculated as follows:

1RM�Wt/(0.533�0.419e�0.055�reps),

where “Wt” is the resistance used in the last set in which between 3 and 8 repe- titions were completed, and “reps” is the number of repetitions completed in the last set. This method of establishing the 1RM has been documented in previ- ous SCI resistance training studies34,36,42

and is used to establish a safe starting point for CRT.

The testing protocol for the initial visit consisted of up to 10 warm-up repeti- tions for each CRT exercise at a mini- mum resistance. The protocol for tradi- tional hand positions was followed for the chest press, overhead pulldown, and downward press and was selected based on the manufacturer’s recommended position (Appendix). The manufacturer’s recommended position for the horizon- tal row and overhead press were not explicit; therefore, the traditional hand positions were selected during pilot test- ing based on collective user preference. Testing was completed using the partic- ipant’s custom-designed wheelchair, each exercise was completed over 6 sec- onds and timed with a metronome, and 5 minutes of rest was allotted between exercises.

During the second session, scapular and glenohumeral kinematic data were acquired during CRT performed at a resistance set at 50% 1RM. One set of 10 repetitions using both a traditional hand position and a modified hand position for each CRT exercise was assessed (Appen- dix). The modified hand position was selected following pilot testing and based on the ultimate goal of maximizing overall favorable shoulder kinematics (scapular posterior tilt, upward rotation, or external rotation or glenohumeral external rotation) for each exercise. Modified hand positions were within the capacity of the equipment. The order of testing (traditional and modified hand positions) for all 5 CRT exercises was randomized to minimize potential sys- tematic effects of fatigue. Similar to the initial visit, all participants were tested in their custom-designed wheelchair, each exercise was completed with a 6-second pattern, and 5 minutes of rest was allot- ted between hand positions and exercises.

Data Collection (Instrumentation) An electromagnetic system (Flock of Birds mini-BIRD model 800, Ascension Technology Corp, Milton, Vermont) was used to collect 3D shoulder kinematic data during CRT at 100 Hz. Due to the

Figure 1. Mechanical impingement ranges and potential structures. (A) Subacromial Impingement: Lower ranges of humerothoracic elevation (45°– 60°). May impinge on the supraspinatus tendon, infraspinatus tendon, long head of the biceps tendon, and subacromial bursa. (B) Internal Impingement: Higher ranges of humerothoracic elevation (above 105°). May impinge on the supraspinatus tendon, infraspinatus tendon, labrum, and joint capsule.

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configuration of the CRT equipment and ease of access, the left upper extremity was tested. Electromagnetic surface markers were taped to the skin overlying the manubrium, superior surface of the acromion, and distal humerus via a ther- moplastic cuff (Appendix). The reliabil- ity and accuracy of surface marker measures of shoulder kinematics with electromagnetic systems have been described previously.25,26,43– 45

Consistent with previous investigations in our laboratory,32,39 International Soci- ety of Biomechanics standards, modified to include the posterior acromioclavicu- lar notch rather than the posterior lateral acromion, were used to digitize bony anatomical points on the thorax, scapula, and humerus.46 These digitized anatomi- cal points were used to transform sensor data to clinically relevant joint coordi- nate systems (the humerus with respect to the scapula and the humerus and the scapula with respect to the thorax). Scapular orientation relative to the tho- rax was described as internal/external rotation (z-axis), downward/upward rotation (y-axis), and anterior/posterior tilt (x-axis). Glenohumeral orientation relative to the thorax was described as internal/external rotation (z-axis) (Fig. 2).

Data Analysis Descriptive statistics were used to ana- lyze the demographic variables for the sample, including age, sex, body mass index, years after SCI, and number of transfers per day. Because of the poten- tial (but unknown) effect on kinematics, the following covariates were consid- ered: sex, arm dominance, level of injury, body mass index, floor-to- acromion height, and arm length. Cova- riates of potential interest were first assessed for correlation with the depen- dent variables. If covariates did not reach a threshold of at least 0.5 and demon- strate consistent correlations across lev- els of a factor, they were not entered into the model. If entered, the specific cova- riate was retained if significant (P�.05) in the particular model.

The kinematic data for the 10 repetitions for each exercise and with each hand position were averaged across compara- ble humeral elevation angles during the concentric phase synchronized with the metronome. All 5 exercises were per- formed between 30 and 78 degrees of humerothoracic elevation and were con- sidered the lower-range exercises for this study. Two CRT exercises were per- formed between 102 and 120 degrees of humerothoracic elevation and were con- sidered the upper-range exercises. These lower and upper ranges were selected to

most closely approximate impingement risk ranges corresponding to subacro- mial and internal impingement, respec- tively, while still incorporating exercises completed in a portion of that range. Ranges of humerothoracic elevation from 30 to 78 degrees (lower range) and from 102 to 120 degrees (upper range) were selected to represent angles corre- sponding to subacromial and internal impingement potential, respectively. Humerothoracic elevation angles were adjusted from 45 to 60 degrees (lower range) and from 105 to 120 degrees (upper range) to incorporate all relevant exercises and participants. Data were assessed for normality and variance homogeneity. If non-normal data were present, appropriate transformation methods were utilized.

A 2-way repeated-measures analysis of variance (ANOVA) with factors of hand position (traditional and modified) and exercise (overhead pulldown, over- head press, chest press, horizontal row, and downward press) was used to deter- mine the effects on each dependent vari- able (scapular anterior/posterior tilt, upward/downward rotation, and inter- nal/external rotation and glenohumeral internal/external rotation) at the lower range. Ultimately, the participant’s sex was the only covariate entered into the model with adequate correlation, and this was exclusively for glenohumeral internal/external rotation at the lower range.

A second 2-way repeated-measures ANOVA with factors of hand position (traditional and modified) and exercise (overhead pulldown and overhead press) was used to determine the effect on each scapular and humeral dependent vari- able at the upper range. The other 3 exercises (chest press, horizontal row, and downward press) were not per- formed in the upper range. In the event of a significant interaction, pair-wise comparisons with Bonferroni correction for each ANOVA were used to explore the effect of one factor (exercise) at each level of the other factor (hand position). The threshold value for significance was set at P�.05. When the assumption of sphericity was violated for the interac- tion term, as demonstrated by the

Figure 2. Scapular and glenohumeral kinematics. Posterior view of right scapula and humerus. Poten- tially detrimental directions for scapular and glenohumeral kinematic rotations highlighted with the arrow. Figure 2 originally published in: Riek LM, Ludewig P, Nawoczenski DA. How “healthy” is circuit resistance training following paraplegia? Kinematic analysis associated with shoulder impingement risk. J Rehabil Res Dev. 2013;50:861– 874.

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Mauchly test, Greenhouse-Geisser adjusted P values were used. Statistical analysis was performed using IBM SPSS Statistics for Windows, version 19.0 (IBM Corp, Armonk, New York). Sample size was based on a power analysis to detect angular differences across conditions or exercises of 10 degrees or more with 80% power, based on standard devia- tions of 12 degrees or less. This is a con- servative estimate for the statistical power of main effects for these analyses for variables such as scapular and gleno- humeral internal/external rotation, which demonstrate the largest variance. Adequate power was present with this sample size to detect smaller condition or exercise differences for other variables.

Results Kinematic data were lost on 2 partici- pants, resulting in the analysis on 18 par- ticipants (14 men, 4 women; mean age�16.1 years, SD�8.8). Additional participant characteristics are presented in Table 1. Kinematic results are pre- sented for lower-range and upper-range humerothoracic elevation. Partial eta squared (�2) is reported as a measure- ment of effect size.

Kinematics: Lower Range (30°–78°) Scapular anterior/posterior tilt. A kinematic summary of scapular anterior/ posterior tilt is displayed in Table 2 and Figure 3 (graph A). There was no exer- cise � hand interaction. There were sig- nificant main effects for hand position (F1,17�5.8, P�.028, partial �

2�.3) and exercise (F4,68�12.9, P�.001, partial �2�.4). Specifically, with exercise col- lapsed, the modified hand positions had significantly more scapular anterior tilt versus traditional hand positions. With hand position collapsed, the downward press had significantly more anterior tilt than all other exercises. The chest press had significantly more scapular anterior tilt than the overhead press.

Scapular internal/external rota- tion. A kinematic summary of scapu- lar internal/external rotation is displayed in Table 2 and Figure 3 (graph B). There was a significant interaction effect for exercise and hand position

(F2.395,68�15.3, P�.001, partial � 2�.5).

To compare hand position by exercise, the modified hand position for chest press, overhead pulldown, and overhead press each had significantly more inter- nal rotation versus the traditional hand position. The modified hand position for downward press had significantly less internal rotation versus the traditional hand position. To compare exercise by hand position, for the traditional hand position, the overhead press had signifi- cantly less internal rotation than the chest press, overhead pulldown, hori- zontal row, and downward press. For the modified hand position, there were no significant differences among the exercises.

Scapular upward/downward rota- tion. A kinematic summary of scapu- lar upward/downward rotation is dis- played in Table 2 and Figure 3 (graph C). There was a significant interaction effect for exercise and hand position (F4,68�3.3, P�.015, partial �

2�.2). To compare hand position by exercise, the modified hand positions for overhead pulldown, overhead press, and horizon- tal row had significantly more upward rotation versus the traditional hand posi- tion. To compare exercise by hand posi- tion, for the traditional hand position, the horizontal row had significantly more upward rotation than the chest press and downward press. The over-

head pulldown had significantly more upward rotation than the downward press. For the modified hand position, the horizontal row had significantly more upward rotation than the chest press, overhead press, and downward press. The overhead pulldown had sig- nificantly more upward rotation than the chest press and downward press.

Glenohumeral internal and external rotation. A kinematic summary of gle- nohumeral internal/external rotation is displayed in Table 2 and Figure 3 (graph D). Controlling for sex, there was a sig- nificant interaction effect for exercise and hand position (F4,64�4.013, P�.006, partial �2�.2). To compare hand posi- tion by exercise, the modified hand posi- tion for the downward press and hori- zontal row had significantly more glenohumeral external rotation versus the traditional hand position. The modi- fied hand position for the overhead press had significantly less glenohumeral external rotation than the traditional hand position. To compare exercise by hand position, for the traditional hand position, the overhead pulldown had sig- nificantly more glenohumeral external rotation than the chest press, downward press, and horizontal row. The overhead press had significantly more glenohu- meral external rotation than the chest press, downward press, and horizontal row. The horizontal row had signifi-

Table 1. Participant Characteristicsa

Variable n Ratio X�SD Range

Sex (men:women) 14:4

Years postinjury 16.1�8.8 2–28

BMI (kg/m2) 25.7�4.1 18.7–36.0

Self-reported activity level (transfers/day) 18.0�14.3 4–70

WUSPI (0–150) 1.2�2.2 0–8.4

Level of injury

High thoracic (T2–6) 6

Low thoracic (T7–12) 11

Lumbar 1

Extent of injury

Complete (AIS A) 10

Incomplete (AIS B or C) 8

a BMI�body mass index, WUSPI�Wheelchair User’s Shoulder Pain Index, AIS�American Spinal Injury Association (ASIA) Impairment Scale.

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cantly more glenohumeral external rota- tion than the downward press. For the modified hand position, the overhead pulldown had significantly more gleno- humeral external rotation than the chest press, downward press, and horizontal row. The overhead press had signifi- cantly more glenohumeral external rota- tion than the chest press, downward press, and horizontal row. The horizon- tal row had significantly more glenohu- meral external rotation than the down- ward press.

Kinematics: Upper Range (102°–120°) Scapular anterior/posterior tilt. A kinematic summary of scapular anterior/ posterior tilt is displayed in Table 2 and Figure 4 (graph A). There was a signifi- cant interaction effect for exercise and hand position (F1,17�5.358, P�.033, partial �2�.2). To compare hand posi- tion by exercise, the modified hand posi- tion for overhead press had significantly more anterior tilt than the traditional hand position. There was no significant

difference between the modified and tra- ditional hand positions for overhead pull- down. To compare exercise by hand position, for the traditional hand posi- tion, overhead pulldown had signifi- cantly more anterior tilt than overhead press. For the modified hand position, overhead pulldown had significantly more anterior tilt than overhead press.

Scapular internal/external rota- tion. A kinematic summary of scapu- lar internal/external rotation is displayed in Table 2 and Figure 4 (graph B). There was no exercise � hand interaction. There were significant main effects for hand position (F1,17�16.832, P�.001, partial �2�.5) and exercise (F1,17�37.3, P�.001, partial �2�.7). Specifically, with exercise collapsed, the modified hand position had significantly more scapular internal rotation than the traditional hand position. With hand position col- lapsed, the overhead pulldown had sig- nificantly more scapular internal rotation than the overhead press.

Scapular upward/downward rota- tion. A kinematic summary of scapu- lar upward/downward rotation is dis- played in Table 2 and Figure 4 (graph C). There was no exercise � hand interac- tion. There were significant main effects for hand position (F1,17�16.832, P�.002, partial �2�.3) and exercise (F1,17�14.8, P�.001, partial �

2�.5). Specifically, with exercise collapsed, the modified hand position had significantly more scapular upward rotation than the traditional hand position. With hand position collapsed, the overhead pull- down had significantly more scapular upward rotation than the overhead press.

Glenohumeral internal/external rotation. A kinematic summary of gle- nohumeral internal/external rotation is displayed in Table 2 and Figure 4 (graph D). There was a significant interaction effect for exercise and hand position (F1,17�38.086, P�.001, partial �

2�.7). To compare hand position by exercise, the modified hand position for overhead

Figure 3. Mean rotations at lower-range humerothoracic elevation: (A) Scapular anterior/posterior tilt, (B) scapular internal/external rotation, (C) scapular upward/downward rotation, (D) glenohumeral internal/external rotation. Green arrows point to favorable kinematic directions (increased scapular posterior tilt, external rotation, or upward rotation or glenohumeral external rotation). Red arrows point to potentially detrimental kinematic directions (scapular anterior tilt, internal rotation, or downward rotation or glenohumeral internal rotation).

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pulldown had significantly more gleno- humeral external rotation than the tradi- tional hand position. The modified posi- tion for overhead press had significantly more glenohumeral external rotation than the traditional hand position. To compare exercise by hand position, for the modified hand position, overhead pulldown had significantly more gleno- humeral external rotation than overhead press. For the traditional hand position, there was no significant difference for glenohumeral external rotation between the overhead pulldown and the over- head press.

Discussion Upper extremity strengthening is consid- ered a critical element of a comprehen- sive rehabilitation program following SCI. In light of this consideration, exer- cises should be recommended, with an emphasis on healthy shoulder mechan- ics. This study described an in-depth analysis of the 3D shoulder kinematics that occurred during the execution of wheelchair-based, upper extremity CRT

exercises. The unique findings suggest that shoulder kinematics can be favor- ably improved (increased scapular poste- rior tilt, upward rotation, or external rotation or glenohumeral external rota- tion) through selection of hand positions that may positively influence shoulder kinematics during execution of CRT exercises. Currently, there are no other studies that provide recommendations for hand positions that positively influ- ence shoulder kinematics during CRT, nor are there descriptive data on kine- matics during the exercises.

In this investigation, all hypotheses were tested using a threshold at which kine- matic changes ranging between 5 to 10 degrees or greater over comparable humerothoracic elevation angles could influence the subacromial space. This threshold was based on a prior investiga- tion that linked scapular kinematics and the subacromial space.40 Relatively small changes of approximately 7 degrees of scapular protraction, in contrast to retraction (similar to scapular internal/

external rotation in our investigation), were shown to significantly narrow the anterior opening width of the subacro- mial space (located between the anterior aspect of the acromion and the humeral head) by 25%. Although the findings were limited to 4 healthy individuals in static positions, small changes in scapu- lar position equated to decreases in sub- acromial space.40 Our significant findings ranged in magnitude from 1.4 to 18.2 degrees. It may be that some of these changes are not meaningful with regard to affecting the subacromial space. Little is known about the relationship between angular kinematic changes and impact on rotator cuff mechanical impingement, and more investigation is needed. The angular change needed to affect the sub- acromial space also varies across individ- uals depending on their anatomy and glenohumeral kinematics during a spe- cific exercise. The measurement system has an angular accuracy of 0.5 degrees. Because the instrumentation error is less than a degree, we do know that changes

Figure 4. Mean rotations at upper-range humerothoracic elevation: (A) Scapular anterior/posterior tilt, (B) scapular internal/external rotation, (C) scapular upward/downward rotation, (D) glenohumeral internal/external rotation. Green arrows point to favorable kinematic directions (increased scapular posterior tilt, external rotation, or upward rotation or glenohumeral external rotation). Red arrows point to potentially detrimental kinematic directions (scapular anterior tilt, internal rotation, or downward rotation or glenohumeral internal rotation).

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identified in our study were not due to instrumentation error.

In this study, 2 hand positions were com- pared. When compared with the tradi- tional hand position, the modified hand position resulted in a favorable change in shoulder kinematics (in one or more rotations) for 3 CRT exercises (horizon- tal row, downward press, and overhead pulldown). These changes included increased scapular upward rotation (4.6°) for the horizontal row and increased glenohumeral external rota- tion (4.5°) for the downward press (lower range) (Tab. 2, Fig. 3) .The mod- ified position also resulted in increased glenohumeral external rotation (18.2°) for the overhead pulldown (upper range) (Tab. 2, Fig. 4). However, the tra- ditional hand position would be more biomechanically favorable when per- forming the overhead press with increased scapular external rotation (5.5°) and glenohumeral external rota- tion (9.1°) at lower-range humerotho- racic elevation angles (Tab. 2, Fig. 3). The hand position selections (traditional or modified) are simple variations that can be selected by the user during CRT exercise execution and may influence impingement potential.

The downward press machine is one of the most commonly used strengthening machines in SCI centers and is intended to strengthen the muscles used during functional tasks such as the weight-relief raise. The downward press exercise incorporates shoulder movements that are similar to those used in the weight- relief raise. A prior investigation com- pared 3D shoulder kinematics during daily upper extremity weight-bearing activities in individuals with paraple- gia.47 The findings of that study showed increased scapular anterior tilt during ini- tial upper extremity loading of a weight- relief raise and increased glenohumeral internal rotation during both initial upper extremity loading and maximal loading phases of a weight-relief raise.47

In the current study, at the lower range of humerothoracic elevation, the down- ward press exercise performed in the traditional hand position was highlighted as the exercise of most concern, as it had the greatest amount of scapular anterior

tilt and internal rotation and the least amount of glenohumeral external rota- tion and scapular upward rotation.

Mimicking the motion of a weight-relief raise,47 the current study showed the kinematic similarities between the downward press and the weight-relief raise, especially with regard to the degree of scapular anterior tilt at 23.8 degrees and 27 degrees, respectively. If the downward press is necessary to tar- get a specific muscle group, the findings from the current study point to the need for the therapist and individual with SCI to consider alternate movement strate- gies that may minimize harmful shoulder postures while strengthening the muscle groups necessary for successful function. Changes in hand positions may be one strategy that can be considered during the exercise. For example, simple hand placement modifications during the downward press were able to achieve a 5-degree increase in glenohumeral exter- nal rotation and a 4-degree increase in scapular external rotation.

To our knowledge, this is the first project to determine whether shoulder kinemat- ics can be favorably modified during CRT exercises by altering hand position and to ultimately develop specific position- ing recommendations for CRT exercises that emphasize healthy shoulder mechanics (Appendix). Considering the impact of shoulder impingement on function and quality of life following paraplegia, exercise recommendations must thoughtfully include a rationale that encompasses healthy biomechanics. Hand modifications are just one modifi- cation that may influence shoulder bio- mechanics and ultimately reduce impingement risk.

Modifications of trunk position through wheelchair and seating alterations or CRT equipment design also may influ- ence shoulder biomechanics and reduce impingement risk. Participants in this study were allowed to sit in their own custom-designed wheelchairs to mimic the natural environment. Additionally, accessibility issues are the reality of what individuals with SCI encounter on a reg- ular basis when participating in an exer- cise program. Although Cybex Total

Access equipment (Cybex International Inc, Medway, Massachusetts) was used during this study, it was determined that not all of the upper extremity equipment provided “total access” for all manual wheelchairs. For example, the horizontal bar on the solid back of rigid wheelchairs prevented some wheelchairs from being able to fully access the equipment. These accessibility issues may have contributed to detrimental positioning for some par- ticipants and ultimately kinematics that increased impingement risk. Improved accessibility may have the potential to improve scapular and glenohumeral kinematics and ultimately decrease shoulder impingement risk during CRT.

There are limitations to this study. The current literature regarding kinematics and impingement does not imply causal inference. For instance, it is unknown whether faulty kinematics cause impingement or whether pre-existing impingement causes altered kinematics. Furthermore, it is presumed that more “favorable” kinematics will increase the subacromial space. However, without 3D modeling, it is not possible to verify the impact of multiplanar scapular and glenohumeral motion on subacromial space during the execution of CRT. Also, kinematics were assessed with electro- magnetic surface markers overlying bony prominences, which creates the possibil- ity of skin motion artifact, especially at ranges exceeding 120 degrees of humerothoracic elevation. For this rea- son, the analysis was conducted below 120 degrees of humerothoracic eleva- tion, which reduces the impact of skin motion artifact.43 Finally, variable wheel- chair seat heights may influence shoul- der positions. However, allowing partic- ipants to sit in their own custom- designed wheelchairs was purposefully selected to mimic the natural environment.

This study provides the foundation for future studies, including a clinical trial for individuals with impingement and application to other strengthening pro- grams. Future research is needed to investigate shoulder kinematics with other brands of CRT equipment, beyond Cybex Total Access. Future research also is needed to assess the effect of modifi-

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cations beyond hand position, including improved postural stabilization or addi- tional hand options, on shoulder kine- matics during CRT. Finally, 3D modeling should be performed to verify the impact of multiplanar scapular and glenohu- meral motion on subacromial space dur- ing the execution of CRT.

In summary, varying hand positions alter shoulder kinematics during CRT exer- cises that are more biomechanically favorable. When possible, CRT hand positions and exercises should be cho- sen that emphasize healthy shoulder mechanics, with the goal of increasing scapular external rotation, upward rota- tion, or posterior tilt or glenohumeral external rotation.

Dr Riek, Dr Ludewig, and Dr Nawoczenski provided concept/idea/research design. Dr Riek and Dr Nawoczenski provided writing and project management. Dr Riek and Mr Tome provided data collection. Dr Riek, Dr Nawoczenski, Mr Tome, and Dr Ludewig provided data analysis. Dr Riek and Dr Nawoczenski provided project manage- ment. Dr Nawoczenski provided facilities/ equipment and institutional liaisons. Dr Ludewig and Dr Nawoczenski provided con- sultation (including review of manuscript before submission).

The authors thank the Pieters Family Life Center, SCI community of western New York, and Dr Jonathan Riek for their assis- tance with this project.

DOI: 10.2522/ptj.20140602

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Appendix. Circuit resistance training exercises using wheelchair-accessible Cybex Total Access (Cybex International Inc, Medway, Massachusetts) and Endorphin Parallel Dip (Endorphin Corp, Pinellas Park, Florida). Recommended hand positions based on clinically meaningful differences between hand modifications. Appendix (modified) originally published in: Riek LM, Ludewig P, Nawoczenski DA. How “healthy” is circuit resistance training following paraplegia? Kinematic analysis associated with shoulder impingement risk. J Rehabil Res Dev. 2013;50:861– 874.

Overhead Press

Traditional Hand Position Modified Hand Position Recommended Hand PositionStart End Start End

Traditional

Instructions: Grasp horizontal handles and press straight up. Instructions: Grasp perpendicular handles and press straight up.

Chest Press

Traditional Hand Position Modified Hand Position Recommended Hand PositionStart End Start End

Either

Instructions: Adjust handle position so that, when grasped, upper arms are straight to side. Grasp horizontal handles. Keep elbows out to the side, level with handles. Extend elbows.

Instructions: Adjust handle position so that, when grasped, elbows are at the side. Grasp vertical handles. Keep elbows at side. Extend elbows.

(Continued)

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Appendix. Continued

Overhead Pulldown

Traditional Hand Position Modified Hand Position Recommended Hand PositionStart End Start End

Modified

Instructions: Set handle position height and adjust thigh pads for stabilization. Grasp bar outside shoulder width with palm down, lean back at hips, and pinch shoulder blades down and back. Bend arms, bringing bar down in front of face, and return elbows to side of body.

Instructions: Set handle position height and adjust thigh pads for stabilization. Grasp bar outside shoulder width with palm up, lean back at hips, and pinch shoulder blades down and back. Bend arms, bringing bar down in front of face, and return elbows to side of body.

Horizontal Row

Traditional Hand Position Modified Hand Position Recommended Hand PositionStart End Start End

Modified

Instructions: Adjust chest pad to allow grasp of handle with arms fully extended. Feet on footrest. Grasp horizontal handles. Pinch shoulder blades throughout and contact chest pad. Bend arms and bring elbows beside body with elbows up.

Instructions: Adjust chest pad to allow grasp of handle with arms fully extended. Feet on footrest. Grasp vertical handles. Pinch shoulder blades throughout and contact chest pad. Bend arms and bring elbows beside body.

Downward Press

Traditional Hand Position Modified Hand Position Recommended Hand PositionStart End Start End

Modified

Instructions: Center machine with handles between greater trochanters and lateral femoral condyles. With thumbs pointing forward, grasp forward-facing handles. Lean forward off backrest with head centered over mid-thighs. Press straight toward the floor with elbow extension and shoulder depression.

Instructions: Center machine with handles between greater trochanters and lateral femoral condyles. With thumbs pointing forward, grasp lateral-facing handles. Lean forward off backrest with head centered over mid-thighs. Press straight toward the floor with elbow extension and shoulder depression.

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