Muscle activity and spine load during anterior chain whole body linkage exercises: the body saw, hanging leg raise and walkout from a push-up
Stuart McGill, Jordan Andersen, & Jordan Cannon
A review by James Shmagranoff
Introduction
Full body linkage, as opposed to open and closed chain exercises, has been shown to increase functional strength. In an attempt to minimize joint wear, body linkage exercise offer both muscle activation as well as joint loading throughout the linkage instead of focusing on one particular joint. In regards to the torso, by utilizing exercises that prevent joint movement, stiffness in the spine (stability) and proximal stiffness can offer more resilience to spine buckling and allow for a focus of power and quickness in the arms and legs. In addition to that, stiffness can also be used not only as load bearing, but for movement control and limb power production. In order to provide some insight into how whole body linkage exercises in terms of three-point bend, distraction tension, and high compression bend affect the spine and muscle activity, the study utilized the body saw, hanging leg raise, and walkout from a push-up. This study hopes that its findings will help with individualized exercise programming of those who have issues with spine loading, injury compromising, and targeting muscle activation. The focus was kept to lower back loading, as many athletes have pain in this area.
Methods
The study utilized 14 males from a university of average of age of 21.1 years, height of 1.77m, and weight of 74.6kg. The study was approved through the Office of Human Ethics and each participant signed over consent.
Instrumentation: Electromyography electrodes monitored muscle activity and 3D markers were placed throughout the body to track movement. The information was then put into a 3D model that utilized information gathered from the electrodes and markers to estimate the force of the muscles. This method allowed for each participant to use their own choice of motor control on each exercise. Spine loads were calculated using muscle forces and joint linkages.
Electromyography (EMG): The body sites were prepared by shaving and cleansing the area. Fifteen electrode pairs were placed parallel to the muscle fibers at specifically measured locations in regards to muscles and point of reference. For example, one pair was placed on the right side rectus abdominis 3cm lateral to the navel. To allow for the most detailed monitoring, only half of the body was used to record results, since it was presumed that there would be symmetry among both sides in regards to motor control. Motion capture software was used to relay the information gathered from the EMG.
Maximal voluntary isometric contractions (MVC) for normalization to activate muscles isometrically while reducing back injury and avulsions were completed by all participants. The rectus abdominis, internal and external obliques were normalized by utilizing a specific sit-up posture of 45° torso and 90° flexed hips and knees and then by performing right and left twists and bends as wells as a maximal isometric flexion movement. The latissimus dorsi utilized a static hold during a pull-up for normalization. The gluteus maximus and spine extensors utilized the Biering-Sorensen position for normalization. MVC was performed by specific movements on the quadriceps, gluteus medius, biceps brachii, trapezius, triceps, anterior deltoid, pectoralix major, and serratus anterior. The normalization measurements were used as the maximal activation for each particular muscle.
Kinematics and placement of markers: Reflective markers and rigid bodies were placed at 28 sites to track the kinematics of the segment linkages so the motion detection system could track the reflective markers’ coordinates.
Exercises and description: A metronome and a research assistant aided in maintaining steady movements. Except for the walkout, which was done at the individual’s pace, each exercise was completed three times in a 2-1-2 count.
1. Body saw: with feet held in straps, knees bent, and forearms supporting body weight on the ground, each participant straightens the legs, holds, and brings legs back to body
2. Leg raise: while holding on to an overhead bar, the spine is held neutral while knees are raised to make a 90° hip angle, held, and released
3. Leg raise with knees straight: while holding on to an overhead bar, the spine remains neutral and legs are extended to create a 90° hip angle without bending the knees, held, and released
4. Walkout: starting in a push-up position, the hands are walked forward as far as possible, held, and then walked back.
Data analysis: EMG was used to model spine muscle activation, while kinetic and kinematic data predicted the back loads. The latter was completed by utilizing software that documented the markers and calculated the angles of the spine curvature and forces and reaction moments on the lumbar spine. The information allowed for modelling stages that consisted of arms, legs, and torso linked segment modeling; 3-D ribcage, pelvis, and vertebrae lumbar spine modeling for stiffness and strain; muscle force and muscle stiffness modeling; intervertebral joint moments and muscle force/stiffness profiles.
Being able to specifically model to each individual allowed for sensitive muscle activation sensing. EMG and spine load were calculated in the following four phases:
1. M1- Midway-while halfway to full extension/legs raised
2. P-Peak-at full extension/legs completely raised
3. M2-Midway2- between peak and release to rest
4. E-End-rest position
Results
The abdominal wall was challenged greatest by the hanging straight leg raise, measuring greater than 130% of the MVC in the rectus abdominus, 88% of MVC in external oblique, and 110% of the MVC in the pectoralis major. Dynamic exercises tend to be greater than isometic exercises, thus receiving results greater than 100% of MVC is not uncommon. The rectus abdominus was activated highly in all anterior chain exercises. External obliques were activated greater than internal in each exercise. The hanging straight leg raise had high activation in the pectoralis major. The body saw activated the serratus anterior 140% MVC. The body saw had the least spine compression at less than 2500N.
Discussion
The exercises chosen did not put a taxing load on the spine, but all exercises did have high activation of the rectus abdominis. External obliques do not create the stiffness utilized in load bearing exercises, but they do provide more push and flexion of the torso. In regards to the push-up, the body saw showed similar loading but utilized cyclic hip and abdominal activity. The participants did not tend to have many differences in regards to variability throughout the exercises, which could have allowed for more participants, as this study had limitations due in part because only a small number of healthy, fit males were utilized. However, differences in height might affect the joint moments. The data collection and instrument calibration was also extensive in regards to labor and time. Female participants are planned to be used in further studies. The purpose of this study was to utilize the data found in how each exercise affects the spinal load and activates the muscles. This information can be used when creating exercise programming for individuals based on injury, goals, and athletic level.
Practical application
Any research that’s purpose is to directly relate the effect an exercise has on load bearing technique and muscle activation is a great tool for the development of individualized routines because a trainer always wants to give the client the best possible program to avoid injury and obtain their goals. It is not uncommon for fitness trainers today to work with athletes at varying levels with a large number of injuries. It has been very disconcerting in my own professional career to work with many younger individuals with a large degree of injuries, all of which were caused by a combination of faulty movement patterns and/ or terrible coaching on movement technique from their previous coaches and trainers. These types of studies provide fitness professionals working at different capacities with athletes and clients with applicable information on how to work around these injuries and still obtain optimal results on how to achieve maximum activation of muscle groups. This information is key to trainers who work with both injured and non-injured clientele.
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