Updated: Mar 19, 2020
In the previous post we discussed the theory behind Problem detection traffic light system and what information can be brought up with it. Today we wanted to discuss more about how this feature can be implemented in real-life training and what benefits does it bring to the user. As we have mentioned previously, our traffic light system is very visual and the amount of bilateral asymmetry is easily investigated. When left-right difference is detected with EMG, it may be because of various reasons and its origin should be sought with caution. Asymmetry may occur because of strength difference between legs and left-right muscle groups. Stronger muscle has more large fast twitch muscle fibers than weaker one and can therefore create higher EMG values. On the other hand, tight or stiff muscle sends easily stretch reflex when stretched and this is seen in EMG as higher value. In addition, tightness in stabiliing muscles may inhibit their function and force superficial muscles (that we measure with surface EMG) to take their role. The same kind of compensation is often seen in synergist muscle groups because of learned movement patterns, muscle tightness and therefore inhibition. Often injuries lead to these changed movement patterns that may remain chronic if nothing is done to change them back with corrective actions. Mobility restrictions, technique, leg length differences and pelvis position should also be considered as candidates when the origin for bilateral muscle asymmetries is investigated. Knowing the athlete and his / her history helps with diagnosis and choosing the corrective actions to restore symmetry.
Quadriceps and hamstring muscle groups are the main muscle groups to control knee and hip joint movements and therefore leg muscle work and function. Both quadriceps and hamstrings increase EMG activation with increasing exercise intensities involving leg muscle work e.g. during cycling and running (Camic et al. 2015). However, the quadriceps to hamstrings relation (Q/H ratio) differs between sports and exercise intensities.
Q/H ratio in running Q/H activation ratio decreases during running speed meaning that when running intensity increases from low speed jogging to maximal sprinting, relatively more and more work comes from hamstring muscles (Camic et al. 2015). Low Q/H strength ratios have been reported in highly trained runners compared to recreational female runners and low Q/H strength ratio is also associated with good running economy independent of fitness level (Sundby & Gorelick 2014). Therefore, it is suggested that runners should consider implementing hamstring exercises, and more specifically eccentric exercises, to improve their Q/H ratios (Sundby & Gorelick 2014). It must be noted that purely strong hamstring muscles does not seem to be an important factor in good running performance and economy but what really matters is the balanced ratio between quadriceps and hamstrings (Sundby & Gorelick 2014). With Myontec Mbody Q/H activation ratio can be assessed during running with different speeds to check if activation increases as it should and if Q/H activation ratio decreases with increasing speed. In addition, with Mbody it is possible to find the best exercises to improve hamstring activation and therefore optimie running training. In figure 1 there is quadriceps and hamstring activation measured with Mbody during treadmill running. First intensity is easy jogging and the running speed increases thereafter until exhaustion. Both muscle groups increase activation with increasing running speed but hamstring activation increases more and therefore Q/H activation ratio decreases with increasing running speed. This is an example of good leg muscle work during running. According to our own tests with highly trained athletes, the optimal Q/H activation ratio during slower intensity endurance running is 45/55 % and with higher speed running 40/60 %. In sprint running the Q/H ratio increases up to 30/70 % in highly trained sprinters. With Mbody Live the Q/H ratio can be monitored real-life during you training to see that correct technique is maintained throughout intensities and fatigue accumulation.
Q/H ratio in cycling During cycling the Q/H ratio is closer to 50/50 % or quadriceps typically dominate hamstrings with few percentages. However, cycling techniques and muscle activation vary a lot due to power output, pedaling rate, body position, shoe–pedal interface, training status and fatigue (Hug & Dorel 2009). It does not seem to be clear, which technique is the most efficient. An exercise physiologist Patty Tomlin from Colorado’s Boulder Center for Sports Medicine sees that the common problem in many cyclists is they have overdeveloped quadriceps muscles and weak hamstrings, and the role of hamstrings during pedaling is generally underestimated. Quadriceps dominant pedaling leads into a loss of power due to fatigue, and a greater chance of back pain, or even injury. The hamstring link is key, concludes Tomlin (Furya 2011, 159). During cycling you want to produce your power at the hips, not the knee joint and therefore the role of hamstrings is crucial during power phase when knee hip extends and not recovery phase, as generally believed, describes James Wilson in his Manifesto (Wilson). Figures 2 and 3 illustrates the activation patterns of variety of leg muscles during cycling.
Relaxation level Both during running and cycling the working leg muscles activate cyclically during gait cycle or pedal stroke, respectively. That means that muscles activate and then relax before new activation cycle. Repeated muscle activations eventually cause fatigue when performed either for long durations or with high intensities. Muscle fatigue is characteried e.g. by slowed and impaired relaxation. In addition, muscle cramps also impair muscle relaxation level. Proper relaxation between activation cycles is essential for efficient muscle function. With Myontec Mbody Relax-parameter relaxation level and therefore the functional state of muscles can be monitored during training and therefore notice fatigue accumulation. Relax-parameter follows traffic light coding: Green when relaxation level is < 12 V indicating proper relaxation Yellow between 12-20 V when there is a tendency for impaired muscle relaxation Red when relaxation level is > 20 V indicating impaired muscle relaxation
REFERENCES Camic C.L., Kovacs A. J., Enquist E. A., McLain T. A. & Hill E. C. (2015). Muscle activation of the quadriceps and hamstrings during incremental running. Muscle & erve 52 (6); 1023-1029. Furya E. (2011) (editor). The big book of bicycling: Everything you need to know, from buying your first bike to riding your best. Rodale Inc. USA. Hug F. & Dorel S. (2009). Electromyographic analysis of pedaling: A review. Journal of Electromyography and Kinesiology 19 (2009); 182–198. Knapik J.J., Bauman C.L., Jones B.H., Harris J.M. & Vaughan L. (1991). Preseason strength and flexibility imbalances associated with athletic injuries in female collegiate athletes. Am J Sports Med 19 (1); 76-81. Sundby Q.H. & Gorelick M. (2014). Relationship between functional hamstring: quadriceps ratios and running economy in highly trained and recreational female runners. Journal of strength and conditioning research 28 (8); 2214-27. Wilson, J. Flat pedal revolution manifesto. The science and logic behind using flat pedals to become a better rider. http://www.bikejames.com/wpcontent/uploads/2015/01/Flat-Pedal-Revolution-Manifesto.pdf