1. Charles J. Ramos, DHSc, ATC, CSCS, CKTP Saturday February 23, 2019
The Effects of Cross Education on Healthy Populations’ Shoulder External Rotation Strength
Charles J. Ramos, DHSc, ATC, CSCS, CKTP
Saturday February 23, 2019

2. Learning Objectives List the basic concepts of Cross-Education
Choose the correct training methods to induce Cross-Education
Identify the expected outcomes of Cross-Education

3. Background
Cross-education is a phenomenon that involves training one limb in order to increase the strength of the contralateral, untrained, limb
In some cases up to 50% of strength is transferred
There is evidence that cross- education could limit the amount of strength loss during an immobilization period in injured populations
Through cross-education, strength may be retained and restored more effectively in injured and stroke populations
(Farthing & Zehr, 2014; Hendy, Spittle, & Kidgell, 2012)

4. Limb Immobilization
In military, “muscle unloading” caused 10.9% decrease in maximal isometric voluntary contractions of knee extensors after 8 days (Thorlund et al., 2011)
In near-zero gravity conditions, astronauts experienced up to an 11.4% muscle volume decrease of the knee flexors after a 16-day flight (Akima et al., 2000)
Patients sustaining distal radial fractures retained only 50% strength of the non-fractured arm after 3 months
1 year post-fracture, patients still displayed deficits averaging 12%

5. Neural Adaptations and Cross-Education
Initial strength gains are attributed to increased neural drive, synchronization of motor units, and inhibition of the mechanisms of the golgi tendon organs
Biceps brachii EMG increased by 15.7% after 3 weeks of isoinertial strength training (Buckthorpe et al., 2015)
Tillin et al. (2011) found a 26% increase in EMG after 4 weeks of knee extensor maximal isometric training
-Strength in this phase is increased without the increase of muscle morphology

6. Highlights in Cross-Education: Participants
Post-infarct patients have improved dorsiflexion strength by 31.37% after six weeks of cross-education training (Draghert & Zehr, 2013)
Coombs et al. (2016) found an increase in wrist flexion and extension strength of healthy participants after 3 weeks of cross-education training
In weeks 9-12 after distal radial fractures, cross-education participants experienced 34% greater increase in strength

7. Quiz
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To: 37607

8. What best describes cross-education in the context of injured populations?

9. Highlights in Cross-Education: Direction of Transfer
The direction of strength transfer initially was exclusively observed from dominant limb to non-dominant limb (Farthing, 2009; Farthing, Chilibeck, & Binstead, 2005)
Some research has demonstrated cross-education to be bi- directional (Coombs et al., 2016)

10. Highlights in Cross-Education: Muscle Contraction Type
Eccentric training seems to induce the highest percentage of cross- education strength (Seger & Thorstensson, 2005; Lepley and Palmieri-Smith, 2014)
Concentric and eccentric training are the best options compared to isometric training (Kidgell et al., 2015)

11. Highlights in Cross-Education: Training Protocol
Novel tasks
Concentric and eccentric muscle actions
High intensity and high volume protocol (70%-80% 1-RM, 6-8 repetitions, 4-6 sets)
Between 3 and 12 weeks long
Dragert and Zehr, 2013; Hortobágyi et al., 1997

12. Hypotheses
After 3 weeks of unilateral shoulder strengthening, the dominant arm trained (DA) and Non-dominant arm trained (NA) groups will experience an increase in external rotation strength on the contralateral shoulder compared to the control group
There will be no difference in change in strength between the NA and DA groups
There will not be a difference in change in strength between the trained and untrained shoulders of both training groups

13. Methods (participants)
A randomized controlled trial, pretest-posttest control group design was used to determine the cross-education effects on shoulder strength
The approval of the California Baptist University IRB and the A.T. Still University IRB was obtained before data collection
There were 21 recruited participants with an average age of 18 – 24 years from a NCAA DII university
The inclusion criteria allowed for collegiate students between the ages of 18 – 35 years
Potential participants were not included if they had a significant neck, shoulder, elbow, or wrist injury in the past 6 months
The participants were randomly assigned to a control (CON), non- dominant arm training (NA), or dominant arm training (DA) group.

14. Handedness, left/right
Participants
Demographic Characteristics of Shoulder Training Participants
Mean (±SD)
Training protocol
Participants, % (n)
Sex, women/men
Handedness, left/right
Age, y
Height, cm
Mass, kg
TSC
Control
42.9 (9)
4/5
0/9
20.8 (±1.7)
174.4 (±7.6)
78.6 (±11.4)
0 (±0) NA
28.6 (6)
4/2
0/6
21.1 (±2.1)
171.4 (±13.4)
75.3 (±22.4)
8.17 (±0.8) DA
1/5
2/4
24.2 (±3.1)
171.8 (±13.4)
79.2 (±15.7)
7.83 (±0.9)
Note. Percentages may not add up to 100% due to rounding. TSC = Training sessions completed; NA = Non-dominant arm trained; DA = Dominant arm trained.

15. Methods (Instruments and Testing)
All participants’ shoulder external rotation strength was measured with MicroFET© hand held dynamometer (HHD) (MicroFET 2, Hoggan Health Industries Inc., Biometrics) on both shoulders
The Pearson product moment correlation coefficient between the HHD and an isokinetic dynamometer was an average of 0.74 showing good validity (Johansson et al., 2015)
The HHD has intraexaminer reliability (ICC) with 95% CI of 0.92 ( ) on the non-dominant arm and 0.91 ( ) on the dominant arm (Cools et al., 2016)
The participants were seated with elbow at 90°of flexion and the HHD held against the forearm
When instructed to “make a contraction”, the participants pushed outward against the HHD and tester for 5 seconds

16. HHD

17. Methods (Training)
The DA and NA group participants performed unilateral shoulder resistance training
3 sessions per week for 3 weeks
Shoulder external rotation was performed on a Cybex Bravo pulley system
Each training session consisted of 4 sets of 6 – 8 repetitions at 70% 1-RM with a 1 minute recovery between sets
The CON group did not perform the training, but continued with activities of daily living

18. Training

19. What is the most effective training protocol to induce cross-education effects?

20. Results Peak Shoulder External Rotation Strength (Mean Newtons ±SD)
Trained arm
Untrained arm
Group
Pre-training
Post-training
Control
120.7 ± 47.7
131.5 ± 37.4
128.5 ± 31.0
129.1 ± 26.8 NA
109.2 ± 39.0
150.1 ± 54.0
117.1 ± 33.1
150.5 ± 43.6 DA
145.3 ± 38.0
178.2 ± 46.0
138.0 ± 43.5
166.6 ± 53.0

21. Results Peak Shoulder External Rotation Strength (Mean Newtons ±SD)
Trained arm
Untrained arm
Group (n)
Pre-training
Post-training
Control (9)
120.7 ± 47.7
131.5 ± 37.4
128.5 ± 31.0
129.1 ± 26.8
Comb (12)
127.2 ± 41.1
164.1 ± 49.8
127.5 ± 38.4
158.5 ± 47.0
Comb = Training groups combined (NA + DA)

22. Results
Figure 1. Shoulder external rotation strength of the trained and untrained shoulders before and after 3 weeks of unilateral strength training.

23. Discussion
The untrained shoulders of the training groups increase in external rotation strength
Kidgell et al. (2015); Lepley and Palmieri-Smith (2014)
Arm dominance did not play a role in transfer of shoulder strength
Coombs et al. (2016)
There was no difference in strength gains between the trained and untrained arms of the training groups
Kidgell et al. (2015); Seger and Thorstensson (2005)
We found that when healthy participants that perform shoulder external resistance 3 times a week for 3 weeks with a prescription of 4 sets of 8 at 70 1-RM increased external rotation strength on the non-trained shoulder significantly. We would expect similar results in injured populations, maybe not as prominent. How would this look and what would benefits could we expect for an injured athlete? To speculate, we can say that a good percentage of strength could be transferred over to the immobilized arm. But after a limb is immobilized for several days and up to several weeks, it has been noted that there will be a significant drop in muscle mass, strength, and function. Therefore, at best we could expect an athlete to mitigate the amount of strength loss during a limb immobilization period.
The fact that arm dominance did not play a role in whether or not strength was transferred is important. We found that both groups (NA and DA) increased strength on their non-trained arm from baseline to 3 weeks post. The importance of this finding lies in the notion that an athlete could potentially injure either arm; you don’t get to choose which arm you hurt. Therefore, these findings could apply in any situation.
Finally, when we compared the trained arms to the untrained arms regardless of training group, we found no difference. The importance here is in noting that the increase in strength was similar for both groups. So, if the trained arm increased external rotation strength by 20%, then we would expect a 20% increase on the untrained arm.

24. What outcomes should we expect from cross-education training in different populations?

25. References
Cools, A. M. J., Vanderstukken, F., Vereecken, F., Duprez, M., Heyman, K., Goethals, N., & Johansson, F. (2016). Eccentric and isometric shoulder rotator cuff strength testing using a hand-held dynamometer: Reference values for overhead athletes. Knee Surgery, Sports Traumatology, Arthroscopy, 24(12), 3838–
Coombs, T. A., Frazer, A. K., Horvath, D. M., Pearce, A. J., Howatson, G., & Kidgell, D. J. (2016). Cross-education of wrist extensor strength is not influenced by non-dominant training in right-handers. European Journal of Applied Physiology, 116(9), 1757–
Farthing, J. P., & Zehr, E. P. (2014). Restoring symmetry: Clinical applications of cross-education. Exercise and Sport Sciences Reviews, 42(2), 70–75.
Hendy, A. M., Spittle, M., & Kidgell, D. J. (2012). Cross education and immobilisation: Mechanisms and implications for injury rehabilitation. Journal of Science and Medicine in Sport, 15(2), 94–

26. References
Johansson, F. R., Skillgate, E., Lapauw, M. L., Clijmans, D., Deneulin, V. P., Palmans, T., & Cools, A. M. (2015). Measuring eccentric strength of the shoulder external rotators using a handheld dynamometer: Reliability and validity. Journal of Athletic Training, 50(7),
Kidgell, D. J., Frazer, A. K., Rantalainen, T., Ruotsalainen, I., Ahtiainen, J., Avela, J., & Howatson, G. (2015). Increased cross-education of muscle strength and reduced corticospinal inhibition following eccentric strength training. Neuroscience, 300, 566–
Lepley, L. K., & Palmieri-Smith, R. M. (2014). Cross-education strength and activation after eccentric exercise. Journal of Athletic Training, 49(5), 582–
Seger, J. Y., & Thorstensson, A. (2005). Effects of eccentric versus concentric training on thigh muscle strength and EMG. International Journal of Sports Medicine, 26(01/02), 45–52.

27. Questions?