Do we need to use eccentric or isometric exercises to prevent hamstring injuries and improve sports performance?
Great question and blogpost by Bas van Hooren! š
Bas Van Hooren is a sport scientist, athlete and freelance strength and conditioning specialist from Maastricht, The Netherlands. He graduated from a MSc Human Movement Sciences in Maastricht University in 2016 and is currently looking for funding for his PhD project on novel isometric hamstring exercises.
Bas has written several peer-reviewed publications about various topics in both Dutch and in international journals, but his main interest relates to the transfer of training to sports performance.
He frequently shares new information on various sports science topics on his LinkedIn (https://nl.linkedin.com/in/basvanhooren) and twitter (@BasVanHooren).
It is widely believed that the hamstrings undergo an eccentric muscle fiber action (they are lengthening while being activated) during the swing phase of high-speed running. Therefore, eccentric exercises are being incorporated into training programs to prevent hamstring injuries and improve sports performance as it is thought that they specifically replicate the hamstring functioning during running. However, in a recent review, we argued that there may actually be no eccentric, but rather an isometric hamstring muscle fiber action during the swing phase of high-speed running [1].
Evidence from animal studies
Animal studies directly measured muscle fascicle length changes using sonomicrometry and showed that the hamstrings first passively lengthen and when the muscle fibers are activated later during the swing phase, the tendinous tissues stretch and recoil, while the muscle fibers remain isometric (Figure 1). Therefore, the evidence from animal studies suggests that there is no eccentric muscle fiber action during running.
Figure 1. Biceps femoris fascicle length and electromyographic activity during three strides of slow trotting in a goat. Adapted from Gillis et al. [2].
Evidence from human studies
In humans it is not possible to directly measure muscle fascicle length changes using sonomicrometry. Therefore, fascicle length changes have been estimated using computational modelling studies. In contrast to the animal studies, these modelling studies found an eccentric hamstring muscle fiber action during running. However, these modelling studies did not correctly simulate several mechanical processes such as muscle slack and muscle gearing, which has probably lead to incorrect results [1]. When these mechanical processes would have been correctly simulated, the modelling studies would probably also have found an isometric muscle fiber action (Figure 2).
Figure 2. Actual (possible) hamstring functioning during high-speed running. Adopted from Van Hooren, Bosch [1].
Conclusion and practical applications
There is currently no strong evidence for an eccentric muscle fiber action during running and the evidence from animal studies actually suggest that there is an isometric muscle fiber action [1]. Based on this, it can be argued that high-intensity isometric exercises (see Figure 3 for an example exercise) more specifically replicate hamstrings functioning during high-speed running than eccentric exercises [3]. However, more research is needed to investigate the effectiveness of these isomeric exercises.
For my PhD, I want to investigate the effectiveness of these high-intensity isomeric exercises and the effectiveness of eccentric exercises.
However, Iām still looking for funding, so if you know any sources of funding, then please let me know by sending me a personal message or an e-mail on basvanhooren@hotmail.com !
Figure 3. Single-leg Roman chair hold. Adopted from Van Hooren, Bosch [3].
References
1. Van Hooren B, Bosch F. Is there really an eccentric action of the hamstrings during the swing phase of high-speed running? part I: A critical review of the literature. J Sports Sci. 2016;Epub ahead of print:1-9. doi:10.1080/02640414.2016.1266018.
2. Gillis GB, Flynn JP, McGuigan P, Biewener AA. Patterns of strain and activation in the thigh muscles of goats across gaits during level locomotion. J Exp Biol. 2005;208(Pt 24):4599-611. doi:10.1242/jeb.01940.
3. Van Hooren B, Bosch F. Is there really an eccentric action of the hamstrings during the swing phase of high speed running? Part II: Implications for exercise. J Sports Sci. 2016;Epub ahead of print. doi:10.1080/02640414.2016.1266019.