Shoulder movement involves the synthesis of complex, multijoint information by the peripheral and central nervous system to plan, coordinate, and initiate action in a synergy of afferent and efferent feedback and feed-forward processes (4). As such, overhead athletic performance requires both static and dynamic mechanisms to coordinate glenohumeral and scapulothoracic stability to induce the appropriate motor response (10). Active function is predicated on a sufficient balance of muscular strength, endurance, flexibility, and neuromuscular response to proprioceptive input (2).
Joint position sense plays an important role for the shoulder joint in 2 key components of athletic performance: conscious limb placement and unconscious motor patterning in response to external force during movement (2). Such motor patterns can be characterized as the motor responsiveness to perturbation of the joint. This assists muscular coordination when the shoulder is placed in elevation during overhead activities, where the desired motor pattern response and contractile strength are required for successful performance and attenuation of injury risk (6). It is suggested that efficiency in neuromuscular control to provide responsive stabilization is necessary to sustain high levels of overhead performance and to avoid injury (21). For example, the tennis serve is an athletic technique, which requires coordination of neuromuscular control to optimize performance and to potentially reduce the risk of injury at the point of impact (13).
Structural injury to glenohumeral and scapulothoracic joint positions has been shown to cause deficits in the neuromuscular control response (16,26). For example, rotator cuff injury specifically leads to deficiencies in neuromuscular control, timing, patterning, and strength compared with asymptomatic individuals (5,26). Conversely, in healthy individuals, insufficiencies of neuromuscular control at the glenohumeral joint can often expose ligamentous and capsular tissues to deleterious loads (9). Exposure to vulnerable joint positions with deficient control increases the risk of both acute trauma and overuse conditions (21). Although a comprehensive training regime of resistance training attenuates these risks, overhead perturbation training (OPT) may add additional benefit for those with deficits in overhead control and provide variety and specificity to a sport-specific training regime (22). A training stimulus which facilitates neuromuscular control and speed of response to perturbation has potential to enhance overhead function (25). This is likely through facilitating improved efficiency of synergistic muscle contraction and coordination from proximal to distal through the kinetic chain (17,25). This demonstrates the role of neuromuscular control training in both rehabilitation and prevention of shoulder joint injury. The inclusion of this type of training may improve synchronization of muscle contraction to improve function and possibly reduce injury (8).
The purpose of this article is to present a program of novel exercises to train the neuromuscular control response. This progression series aims to expose individuals to perturbations which may be sufficient to encourage an adaptive training response through updating motor commands with accommodation of successful and error feedback (20). This may be particularly useful for those with deficiencies in upper limb neuromuscular control.
OVERHEAD PERTURBATION TRAINING
Perturbation of upper limb position during overhead activities causes unpredicted change in tissue length, resulting in a responsive pattern of muscular contractions. The exercise series described in this article ensures that the deficient client is exposed to positions of vulnerability against displacement of the limb by external force. It is postulated that neural adaptations are induced through introduction of both rhythmic and sudden alterations to these positions, as seen in both postural responses in ballet dancers (23) and with lower limb neuromuscular training (19). The progressive and graduated exposure of the athlete aims to facilitate physiological adaptive responses to improve neuromuscular motor patterning (2,8). These adaptive responses will occur both in peripheral joint and muscle afferent centers and by central (spinal, basilar, and motor cortexes) mechanisms (6). Furthermore, through exposure, proper force couples can be developed to balance joint forces (3). This dynamic coupling aims to achieve joint stability through efficiency of neuromuscular control rather than through reliance on passive connective tissue (3,8). Muscle afferent feedback can evoke corrective responses within milliseconds of mechanical perturbation (20). This relies on fast feedback loops, inclusive of short-latency stretch reflex, which are sensitive to changes in joint motion (3). The motor system produces a stereotyped sequence of muscle activity when the limb is displaced by a mechanical perturbation, beginning with short-latency stretch reflex (20–50 ms after perturbation) and ending with voluntary response (>100 ms) (3). These are not easily modified by unexpected task demand (perturbation) without extended experience or previous practice (26). In essence, controlled exposure to perturbations may induce adaptive neuromuscular response to improve motor control and theoretically, overhead performance.
The OPT exercise series provides a variation from other overhead lifts by providing a variable challenge and perturbation at the end-of-range position. An example of such an exercise is the Turkish get-up (15). This exercise incorporates a multibody part movement from the supine position through a side plank and a lunge before finishing in standing. This is performed while sustaining a fully elevated shoulder position against resistance. These perturbations assist to develop greater reactive neuromuscular control than other overhead techniques because of the random nature and unexpected force of the stimulus (17). This requires both preparatory muscle activity and reactive muscle activity as the individual responds to the stimulus (17). The OPT “pre-setting position” is chosen at end range of elevation purposefully to optimally challenge joint position sense and motor responses. Janwantankal et al. (10) reported that the ability to reproduce joint positions accurately improves toward end-of-range positions. This is when capsular structures become taught, increasing afferent input and greater responsive muscle activation. However, in the case of individuals with previous injury, joint position sense may remain deficient (14), even if symptoms have resolved. As the OPT exercise series uses the end-of-range position of the shoulder, it is important that all clients and trainers and/or therapists take note of the potential risks of exposure to these movements. Close communication between the client and health care provider and/or exercise trainer is prudent and should be alongside regular observation and feedback to ensure safe performance of the series.
A prerequisite for this exercise series is the availability of full glenohumeral joint elevation. The exposure to a sudden alteration of position at end of range should be performed cautiously, initially with low load for low numbers of repetitions to assess reaction of the individual. Pain and/or inability to maintain the starting position is an indication that this type of training is contraindicated.
THE OVERHEAD PRESS
Secure the resistance (elastic resistance band/lifting band) to a weight/kettlebell (Figure 1A and 1B). The amount of resistance should be predetermined through strength testing at end range elevation. Position the arm in the plane of the scapula with the elbow fully flexed and the palm positioned into desirable grip (palm facing inward or forward) placing the resistance band or handle into the grip (Figure 2A and 2B). The act of gripping (even at 50% of maximal voluntary contraction) has been demonstrated to activate the rotator cuff muscles (1). Within this plane of motion, extend the elbow vertically maintaining appropriate force as the resistance band is placed under longitudinal tension elevating the weight from the ground/platform. The client should resist internal and external glenohumeral rotation to maintain vertical forearm position through the movement until full glenohumeral elevation (flexion) is achieved with the elbow fully extended. This should be sustained without physical compensatory behavior (Figure 3A and 3B). The client should elevate (flex) the glenohumeral joint to the point before compensatory lumbar hyperextension (Figure 3A and 3B). A cocontraction of the upper limb musculature maintains this position (while the banded weight provides perturbation to the upper limb). Resistance should be present at the starting position and remain throughout the entire range. The selection of the load and resistance band is dependent on the experience level of the individual. In this training method, their subjective reports and objective characteristics (e.g., strength and endurance) are taken into account before application. The combination of weight and resistance band extensibility used would modify the magnitude of the perturbations provided. The degree of perturbation stimulated should be at a level that can be sustained without client discomfort or compensation. Loss of glenohumeral joint and scapulothoracic position may indicate compensation because of muscle fatigue and compensatory increases in dominance by other muscle groups (7).
MODIFICATION AND PROGRESSIONS
Modifications can be made to encourage greater specificity of function or to address the client's particular needs. For example, allow substitutions such as varying the degree of internal and external rotation through the movement if correlating to desired rehabilitation or sporting task. Various speed and type of contraction (isometric, concentric, eccentric, and plyometric) can be added based on desired rehabilitation or performance goal. Performance should be evaluated for compensatory movement at the glenohumeral and/or scapulothoracic joints and further along the kinetic chain. Fatigue can manifest peripherally and centrally, which is believed to desensitize muscle spindle threshold and in turn impair joint position sense and subsequent neuromuscular responses (18,24). In addition, clients with lower limb impairments alongside an upper limb deficit may modify their starting position by sitting on a bench or an unstable surface such as a gym ball (11,12).
The progression of these exercises should be guided by any client reports of pain and fatigue. Muscle fatigue decreases active and passive joint repositioning and has been shown to adversely alter joint position sense (24) and impair neuromuscular control (18). Progression can be made in various ways and should involve one or more of the following parameters of exercise: increasing intensity (through the utilization of a heavier weight); incorporating rhythmic perturbations; and/or increasing the magnitude of the weight displacement (by stimulating greater excursion of the weight or by increasing the length of the resistance band used). In addition, further progression can be made by moving from rhythmic perturbations where a pattern of directional stimulus is shown and taught to the individual, to random, sudden perturbations (provided by external force from the trainer). With adequate performance of the press achieved, further OPT progressions can be undertaken through change of the body position. This changes the overhead perturbation into a compound body movement using multisegments of the kinetic chain. The client is to position the arm into the presetting position and then perform variations as directed below.
Press the weighted band as described into the presetting position of the overhead press as described previously. Once the client is comfortable instruct them to walk for a predetermined distance, speed, stride length, or time (Figure 4A).
Press the weighted band as described into the presetting position of the overhead press as described previously. Instruct the client to lunge forward with the opposite leg of the arm that is in the presetting position of the overhead press. Ensure that the foot contacts the ground with the heel and the forefoot. Lower the body by flexing the knee and hip of the front leg until the knee of the rear leg is almost in contact with the floor. Return to the original standing position (Figure 4B).
Press the weighted band as described into the presetting position of the overhead press as described previously. Advise the client to look up at the overhead hand. Laterally shift the hips to the same side as the weighted band, turn the feet out at a 45° angle from the “pre-set” arm, bending at the hip to one side, maintaining lateral shift at the hip, and slowly lean until the floor is touched with the free hand. Instruct the client to sustain visual contact of the overhead hand at all times. The arm does not need to remain perpendicular to the floor; however, the client should be guided to not allow greater than 30° sway. Pause for a desired period after reaching the ground and then return to the starting position (Figure 4C).
Press the weighted band as described into the presetting position of the overhead press as described previously. While maintaining the presetting position, instruct the client to descend into the squat by flexing the hips and knees until at least 90°; pause and return to the starting position (Figure 4D). The client should be directed to look straight ahead during the squatting movement. Complete the desired sets, reps, and speeds as required.
Overhead barbell walk
Press the bar as described into the presetting position of the overhead press using 1 or 2 arms as desired (Figure 5A and 5B). Instruct the client to walk for a predetermined distance and/or time and at a speed and/or stride length and/or cadence which is challenging. Performing the overhead press with 1 arm using a barbell is a task which should be reserved for when the other previously described variations have been mastered. However, this technique may facilitate greater usage of both trunk and shoulder synergist musculature because of the additional instability of the load (12).
Integration of trunk and lower extremity motion into shoulder exercise movements has been demonstrated to have positive effects on the muscle recruitment patterns at the shoulder (11). This makes multijoint movements an important component of upper limb rehabilitation and sport-specific training.
It is important to include specificity when implementing functional activities, thus the above progressions are not a recipe but a consideration based on the client's needs or specific positions of function.
The glenohumeral joint requires a sensorimotor system with the capacity to ensure joint stability through sensory, motor, and central integration (18). OPT challenges the sensorimotor system to respond to changes in joint position with appropriate neuromuscular responses (17). Development and maintenance of efficiency in neuromuscular control may play a role in reducing injuries and promotion of optimal physical performance.
1. Alizadehkhaiyat O, Fisher AC, Kemp GJ, Vishwanathan K, Frostick SP. Shoulder muscle activation and fatigue during a controlled forceful hand grip task. J Electromyogr Kinesiol 21: 478–482, 2011.
2. Borsa PA, Lephart SM, Kocher MS, Lephart SP. Functional assessment and rehabilitation of shoulder proprioception for glenohumeral instability. J Sport Rehabil 3: 84–104, 1994.
3. Cluff T, Crevecoeur F, Scott SH. A perspective on multisensory integration and rapid perturbation responses. Vision Res 110: 215–222, 2015.
4. Diedrichsen J, Shadmehr R, Ivry RB. The coordination of movement: Optimal feedback control and beyond. Trends Cogn Sci 14: 31–39, 2010.
5. Ellenbecker TS, Cools A. Rehabilitation of shoulder impingement syndrome and rotator cuff injuries: An evidence-based review. Br J Sports Med 44: 319–327, 2010.
6. Frank C, Kobesova A, Kolar P. Dynamic neuromuscular stabilization & sports rehabilitation. Int J Sports Phys Ther 8: 62–73, 2013.
7. Fuller JR, Lomond KV, Fung J, Côté JN. Posture-movement changes following repetitive motion-induced shoulder muscle fatigue. J Electromyogr Kinesiol 19: 1043–1052, 2009.
8. Guido JA, Stemm J. Reactive neuromuscular training: A multi-level approach to rehabilitation of the unstable shoulder. N Am J Sports Phys Ther 2: 97–103, 2007.
9. Horsley I. Proprioception and the rugby shoulder. In: An International Perspective on Topics in Sports Medicine and Sports Injury. Zaslav KR, ed. Croatia: In Tech Europe, 493–508, 2012. Available at: http://www.intechopen.com/books/an-international-perspective-on-topics-in-sports-medicine-and-sports-injury/proprioception-and-the-rugby-shoulder
. Accessed: December 13, 2016.
10. Janwantankul P, Magarey M, Jones M, Danise B. Variation in shoulder joint position sense at the mid and extreme range of motion. Arch Phys Med Rehabil 82: 840–844, 2001.
11. Kalantaria KK, Ardestani SB. The effect of base of support stability on shoulder muscle activity during closed kinematic chain exercises. J Bodyw Mov Ther 18: 233–238, 2014.
12. Kohler JM, Flanagan SP, Whiting WC. Muscle activation patterns while lifting stable and unstable loads on stable and unstable surfaces. J Strength Cond Res 24: 313–321, 2010.
13. Kovacs MS, Ellenbecker TS. A performance evaluation of the tennis serve: Implications for strength, speed, power, and flexibility training. Strength Cond J 33: 22–30, 2011.
14. Lephart SM, Pincivero DM, Giraido JL, Fu FH. The role of proprioception in the management and rehabilitation of athletic injuries. Am J Sports Med 25: 130–137, 1997.
15. Liebenson C, Shaughness G. The Turkish get-up. J Bodyw Mov Ther 15: 125–127, 2011.
16. Ludewig PM, Reynolds JF. The association of scapular kinematics and glenohumeral joint pathologies. J Orthop Sports Phys Ther 39: 90–104, 2009.
17. Myers JB, Lephart SM. The role of the sensorimotor system in the athletic shoulder. J Athl Train 35: 351–363, 2000.
18. Myers JB, Wassinger CA, Lephart SM. Sensorimotor contribution to shoulder stability: Effect of injury and rehabilitation. Man Ther 11: 197–201, 2006.
19. Paterno MV, Myer GD, Ford KR, Hewett TE. Neuromuscular training improves single-limb stability in young female athletes. J Ortho Sports Phys Ther 34: 305–316, 2004.
20. Pruszynski JA, Scott SH. Optimal feedback control of and the long-latency stretch response. Exp Brain Res 218: 341–359, 2012.
21. Reinold MM, Curtis AS. Microinstability of the shoulder in the overhead athlete. Int J Sports Phys Ther 8: 601–616, 2013.
22. Saeterbakken AH, Andersen V, Behm DG, Krohn-Hansen EK, Smaamo M, Fimland MS. Resistance-training exercises with different stability requirements: Time course of task specificity. Eur J Appl Physiol 26: 1–0, 2016.
23. Simmons RW. Neuromuscular responses of trained ballet dancers to postural perturbations. Int J Neurosci 115: 1193–1203, 2005.
24. Voight ML, Hardin JA, Blackburn TA, Tippett S, Canner GC. The effects of muscle fatigue on and the relationship of arm dominance to shoulder proprioception. J Ortho Sports Phys Ther 23: 348–352, 1996.
25. Wilk KE, Arrigo CA, Hooks TR, Andrews JR. Rehabilitation of the overhead throwing athlete: There is more to it than just external rotation/internal rotation strengthening. Phys Med Rehabil 8: S78–S90, 2016.
26. Wolpaw JR. Adaptive plasticity in the spinal stretch reflex: An accessible substrate of memory? Cell Mol Neurobiol 5: 147–165, 1985.