Contra – Lateral Effects of Nerves Crossing & Unbalanced Equilibrium in Sport Andrew Charniga

“…There are known knowns, there are known unknowns and there are unknown unknowns: the ones we don’t know we don’t know”. Donald Rumsfeld, 2004

The incongruous mix of professions involved in one  form or another in the training and care of American athletes: coaches, conditioning coaches, academics, doctors, physical therapists, athletic trainers, personal trainers and so forth; all too often creates the conditions where the people who know what they don’t know and act accordingly, precipitate; or at very least exacerbate, the problem of aberrant sport injury.

With that thought in mind, without question an “unknown unknown” effect in the realm of sport is the ‘X’ crossing; or decussation of nerve fibers in the human body; has on balance/equilibrium as well susceptibility and onset of injury. It is common knowledge the right side of the brain controls the left side of the body and vice versa; the left side controls the right side of the body. Electrical impulses from the brain innervating muscles cross over bi – lateral pathways.

Little thought is given; consequently, even less known, what effect this ‘X’ control of movement; especially balance and equilibrium; has on injury susceptibility.

For that matter, maybe the question that should be asked first is why do the ‘wires’ cross? The crossing of nerves from the brain known as decussation, i.e., forming an ‘X’; is even asymmetrical such that “the right side of the spinal cord is larger than the left, independent of handedness.” (Villiemoz,S. et al 2005). This is due to more fibers originating from the left hemisphere of the brain than from the right hemisphere. The crossing of wires may be an evolutionary adaptation to enhance visual motor coordination to avoid danger by “gathering multiple sensory and motor modalities” (Villiemoz,S. et al 2005).

Many think the decussation of nerves evolved when organisms adopted movement along an axis; and, an adaptation to radial symmetry. At any rate, efficacy of sensory motor function is probably the driving factor (Rogers, L., et al 2013).

The Contra – Lateral Effect: a “spillover” of neural drive?

A contra – lateral effect of strength training was first identified in the late 1890s at Yale university. A young woman training grip strength of one hand noticed an improvement of strength in the opposite (contra – lateral) untrained hand. A number of studies over the intervening years have sought to demystify this phenomena. Since there is no increase in the muscle mass of the untrained limb; the increase in strength sans exercise is generally believed to be neural in nature (Hellbrandt, 1951; Rasch, Morehouse, 1957; Gabriel et al, 2006).  

For instance, Hellbrandt  (1951) suggested “a simultaneous discharge of efferent impulses over bilateral pathways” (from Rasch, 1957), could explain the contra – lateral phenomena. Munn, et al, (2003) used the term “spill over” to explain the training effect to the untrained side. In layman’s terms signals from the brain meant for the the right side of the body may “spill over” to affect muscles on the left side – hence the contra – lateral effect.

This training – effect – without – training has been established under rather simplistic and controlled conditions. Those conditions do not begin to emulate the extraordinary complexity involved in dynamic sport; especially elite dynamic sport. An essential question is how this peculiarity of human biology may affect sport performance after injury; or precipitate a new injury, even to the contra – lateral side of the body.

Another phenomenon associated with the ‘X’ crossing of nerves in the human body occurs when an untrained person activates the same muscles on either side of of the body simultaneously. Typically the total maximum force the muscles can exert decreases in untrained and most athletes. For instance, contracting right and left biceps at the same time. If someone is able to lift say 25 kgs with either arm; when both arms are engaged simultaneously the result is not 50 kgs of muscle power; it is less. A facilitation phenomena is not present.

Conversely, this circumstance is not only absent in athletes such as weightlifters and rowers who must use the same muscles on both sides of the body simultaneously;  a bilateral neural facilitation is present, i.e., enhancing the muscle power in the muscles of both sides of the body. Using the same figures of 25 kgs in the above example; the combined result of the weightlifters for instance would exceed 50 kg; even though the maximum strength of each arm individually was 25 kgs.

Peculiarities of the contra-lateral phenomena do not occur exclusively in the laboratory. The real world nature of such manifestations should give pause (although it doesn’t) to coaches, trainers and therapists preparing athletes for competitions from simplistic viewpoints rooted in classrooms and textbooks. This is especially true for what constitutes generally accepted ideas about balance and equilibrium. 

Is there such a thing as reflexive injury?

For instance, there are many instances in football, basketball and others where an athlete suffers an injury to the opposite side (contra – lateral) of the body; or, to the same side (ipsi-lateral) of the body following a prior injury. Is it possible this is a reflexive injury, for want of a better term? For instance, super star quarterback Patrick Mahomes of the Kansas City Chiefs dislocated his right knee after a recent injury to his left ankle, i.e., a  lower extremity injury on the contra – lateral side.  If any thought is given to the contra – lateral nature of the second injury; it is usually dismissed:

“It is unclear whether Mahomes’ latest injury is in any way related to the previous situation with his ankle. Given it is his knee, the injury is believed to be different.”

The otherwise healthy quarterback, prior to injury, would move about coordinating movement of feet, arms, legs, hands to run about, pass, hand off and so forth. Contra – lateral signals from the central nervous system (CNS) become part of a complex coordination structure; both sides of the body work in unison to produce the complex motor patterns of an elite athlete.

Another example of contra – lateral injury is quarterback Tua Tagovaiola who suffered a high ankle sprain to his left ankle, late in 2018. He returned to play some weeks after surgery. He suffered another high ankle sprain to his right ankle 10 months later: a  contra – lateral lower extremity injury. He returned to play within three weeks following the very same tight rope procedure to repair his left ankle in  2018:

“Our physicians performed a successful tight-rope procedure on his right ankle this morning,” Alabama coach Nick Saban said in a statement. “This is the same injury, but the opposite ankle that Tua injured last season. Tua will miss next week’s game against Arkansas, but we expect a full and speedy recovery.”

Upon his return from the second procedure Tagovaiola suffered a far more serious injury dislocating his hip which included a posterior wall fracture. 

The following is a timeline of Tagovaiola’s injuries including the most serious following two surgeries:

/ Tightrope procedure for high ankle (left) sprain 12/2018;

/ Tightrope procedure for high ankle (right) sprain 10/20/2019 {a day after injury};

/ Hip (right) dislocation and posterior wall fracture 11/16/2019.

We should not assume a uniform input to muscles on each side of the body from a simultaneous discharge of efferent impulses from the brain over the ‘X’ crossing of neural wires. Furthermore, even if the discharge of efferent impulses were uniform; it is unrealistic to assume muscles on both sides will produce equivalent, balanced forces.

Consequently, is it possible the psychological duress of competitions may manifest in multiple injuries to one side of the body? For instance,  Kobe Bryant suffered a tibial plateau fracture soon after returning to play following months of rehabilitation for an Achilles rupture; both to his left leg.

So, how does the body of an elite, or any athlete, manage to perform after an injured ankle, foot, or knee; and/or for that matter, with one or more joints taped to restrict motion? Can a “simultaneous discharge of efferent impulses over bilateral pathways” automatically adjust to shifting stress away from an injured segment; enabling an athlete to perform efficiently and safely? Or, just the opposite. Can this simultaneous discharge over bi – lateral pathways contribute to contra – lateral injury or even multiple injuries to one side of the body because the preparation and/or rehabilitation of athletes is carried out under simplistic conditions to ready the injured athlete for linear movement?

An elite quarterback who performs a complex sensory motor skill by moving about to avoid tackle; all the while endeavoring to select and connect with a moving target; logic would dictate, a prior injury, potentially combined with restricted mobility must impact injury susceptibility.   

Figure 1. Elite female weightlifter lifts the barbell with one foot flat on the floor while the heel of the other foot rises. An example of an asynchronous and asymmetrical  effect on  musculature of lower extremities from a “simultaneous discharge of efferent impulses over bilateral pathways? Charniga photos   

Asymmetry, Asynchrony  & Unbalanced Equilibrium in Sport

“According to Dan Pfaff, coach to former world record holder and Olympic champion Donovan Bailey, “every athlete is asymmetrical; our job is to determine their bandwidth for efficiency and intervene when they are outside that bandwidth” (Athletigen ACP conference, 2018

Due in part to faster, higher resolution cameras, algorithms, force plate technology and such, various deviations from what one would logically assume effective postural dispositions of the body to achieve equilibrium have been observed (Charniga, 2019). For instance, super elite runners, Usain Bolt displayed asymmetrical force application from right to left foot; or, 10,000 meter world champion Almaz Ayana was found to have a significant deviation in stride length of  20 cm between right and left legs.

Weightlifters scissors feet in the split technique of the jerk beginning with asymmetrical hand spacing; asymmetrical placement of feet. Shifting the feet to lift the barbell asynchronously and asymmetrically in a fraction of a second, applying force with both hands; all the while straining to lift  a level barbell against asymmetrical supports from placement of feet in the split (Charniga, 2019)

Can many of these examples of unbalanced equilibrium in sport exercises be normal due at least in part to a single source signal from the CNS sent over bi – lateral pathways, i.e., ‘unbalanced equilibrium’ resulting from spill over from simultaneous discharge of impulses? Can ‘unbalanced equilibrium’ be a normal aberration (Charniga, 2019)? That is to say, for some athletes; even the super elite; equilibrium encompasses asymmetrical and asynchronous movements of upper and lower extremities; likewise stances, gaits and so forth; from nervous innervation sent over crossed wires.    

Assumptions, that is to say beliefs, of what constitutes balance and equilibrium in sport are always inextricably linked with even spacing of feet and hands, synchronous and equidistant stride lengths, uniform power outputs from right and left side of body; equal length of extremities and so forth. However, in all probability these assumptions are universally unproven; beliefs based on reasonable logic (Charniga, 2019). 

Generally accepted, logical assumptions, of what constitutes necessary conditions for athletes to achieve balance and equilibrium; to perform safely: a level barbell, uniform foot strike force in sprinting; or uniform stride length between right and left legs, and so forth; are certainly in question.

Can a possible spill over of efferent signals of right to left, or left to right side of the body affect an athlete in a  negative way performing with a previous injury? Injuries typically cause a loss of mobility and function. An injured right ankle, for instance, cannot be expected to function in a rational synergy with an uninjured left. 

Another complication to consider for an injured athlete to return to optimum performance of complex coordination exercises can be the rehab exercises for the injured side carried out in different postures from the regular posture: for instance, exercises seated instead of standing.

  The effect of posture

Figures 2- 3. Female weightlifter lifts weight in the initial phase of the pull with barbell level. As she continues standing out of a crouched posture the barbell tilts to the left. A indication of an imbalance of muscular effort? However, stance, hand spacing and disposition of feet on the floor remain the same. A plausible explanation: bi-lateral efferent impulses from opposite sides of the CNS to contra – lateral limbs may not produce a uniform effect on the barbell with the change in posture. Charniga photos.   

An unpublished research project (Charniga, A.) at the University of Toledo in 1980 established an effect of posture on grip power with a hand dynamometer. Five subjects recorded higher scores grasping the instrument with maximum effort while standing. The same subjects recorded lower scores while seated; regardless of hand or angle of elbow. This is consistent with research of the effect on strength training one and the same muscle group in different postures.

For instance, there is a clear – cut tendency to realize greater gains when tested in the same posture strength training was carried – out. Alterations in neural input to the muscles with changes in posture affecting the “direction of force application” may have broad implications for training athletes with respect to susceptibility to injury and a contra – lateral problem following injury.

For example, muscle balance ratios between hamstring and quadriceps muscles are widely accepted in the USA for injury prevention and rehabilitation. These ratios are unproven and arbitrary; especially as the testing for these ratios such as hamstring to quadriceps are carried out on machines with subjects seated or lying face down.

All to often, athletes are tested and even trained seated on machines to measure, as well as to train hamstring to quadriceps strength, i.e., balance between thigh flexion to extension strength. This practice persists, utilizing in many cases expensive machinery; even though athletes in dynamic sport, with few exceptions; perform standing. Furthermore, it is unclear how training hamstring muscles lying face down or seated will have some prophylaxis effect for athletes running about on a field or court; where flexing and straightening of lower extremities entails far more complexity.

After all, how often does one see an athlete sustain a  hamstring injury lying face – down; or for that matter, seated?  (see “Ankle breakers & Galss – ket – ball” , Charniga, 2019)

A study of track and field athletes over a period of seventeen years found a prior ankle injury increased significantly the likelihood the athlete would experience a hamstring injury of the same leg (Malliaropoulos, N., et al, 2018). The effect on future hamstring injury caused by an amalgamation of people involved in the rehabilitation and strengthening of the injured ankle: doctors, therapists, conditioning coaches, athletic trainers and so forth is never taken into consideration. Likewise not considered the possibility an injury altering effect on contra – lateral (decussation of nerves) control of movements in sport exercises.  

Research of the effect of posture on strength development shows a clear specificity in results. Results obtained from training while seated cannot be expected to be comparable; or for that matter; readily transferable to the same muscle groups deployed in a standing disposition. For instance:

…”those activities which are performed at a similar posture to that of the strength training tend to improve the greatest extent, compared to those performed in dissimilar postures. … may be caused by differing postures affecting the direction of force application of the musculature, thereby altering its neural input. Wilson, G. “The specificity of Strength training: the effect of posture” Eur J of Appl Phsiol (1996) 73:346 – 352

“It will be observed that the increases in strength following isotonic training were considerably larger when the subject was tested in the position in which he practiced the exercises (erect) than when tested in a position (supine) or by a technique (modified Martin) unfamiliar to him. (Rasch, Morehouse, 1957)

What seem to be aberrations in balance; manifest under the extreme conditions in elite sport; occur in the presence of psychological duress; typical of high level competitions. These aberrations in balance and equilibrium are diametrically inconsistent with standard training conditions; especially simple strength training exercises with machines. Now add to the complexity of dynamic sport, contra – lateral control of movements after injury.


“Judge a man by his questions rather than his answers.” Voltaire

What conclusions/answers can be drawn from an essay full of questions? In point of fact, the questions are the conclusions; the answers. How can anyone be sure of what they are doing is correct if they don’t know what they think they know; or, worse yet, don’t know what they don’t know?

As far as susceptibility to injury of an ipsi-lateral  or contra – lateral limb after injury to the opposite or same side of the body are concerned; the effects of bracing, taping, illogical exercises and techniques on subsequent injury susceptibility; or, even precisely how athletes establish and maintain balance/equilibrium: “we don’t know what we don’t know”.


/ Carroll, T., et al, “Contra-lateral effects of unilateral strength training: evidence and possible mechanisms”, Nov 2006

/  Gabriel, D. Kamen, G., Frost, G.,”Neural Adaptations to Resistive Exercise”, Sports Med 2006: 36(2): 133 – 149

/ Rasch, P., Morehouse, P., “Effect of static and dynamic exercises on muscular strength and hypertrophy”, J. Appl. Physiol. II (1): 29 – 34. 1957

/ Munn, J., et al, “Contra- lateral effects of unilateral resistance training: a meta – analysis” J. Appl. Physiol. 96:18691 – 1866, 2004:10.1152/japplphysiol.00541.2003

 / Wilson, G., et al, “The specificity of strength training: the effect of posture”, Eur J Appl Physiol (1996) 73:346-352 

/ Charniga, A., “Equilibrium in Weightlifting”, 2019

/ Charniga, A., Unpublished research project, 1980.

/ Rumsfeld, D., Former secretary of defense of the United States of America


/ Vulliermoz, S., Raineteau, O., Jabavdon, D., “Reaching beyond the midline: why are human brains cross wired?; Lancet Neurol, 4:87-99:2005

/ Rogers, L., Vallortigara, G., Andrew, R. Divided Brains, Cambridge, UK, Cambridge University press, 2013

/ Malliaropoulos, N., et al, “Higher frequency of hamstring injuries in elite track and field athletes who had a previous injury to the ankle – a 17 years observational cohort study” Published online 2018 Feb 26. doi: 10.1186/s13047-018-0247-4 PMCID: PMC5828071

/Astrand, P-O., Rodahkl, K., Dahl, H., Stromme, ZS., Textbook of Work Physiology Human Kinetics, Champaign, IL 2003

/ Vulliemoz, S., Raineteau, O., Jabaudon, D., “Reaching beyond the mid-line: why are human brains cross wired?”, Lancet Neurol 2005: 4:87-99

/“V.S. Stepanov, V.S., PhD., Tmoilov,V.N., MS, “Morphofunctional Causation of the Formation of Stable Styles of the Competition Movements in Weightlifting”,  The P.F. Lescraft Saint Petersburg State Academy of Physical Culture. Translated by Andrew Charniga www.Sportivny

/ Latish, M., Zatsiorsky, V., Biomechanics and Motor Control, Elsevier, New York, 2016