Hamstring recruitment variability
Pablo Marinho reviews this recent paper on hamstring recruitment variability
The hamstring muscle has been subject of many studies as its injury rates (around 20-40%) and this is of interest for all involved in sports performance. This recent published study has used functional MRI to find out more about its pattern of recruitment after a high load fatiguing task.
Running and Football seems to be top hamstring injury related sports, due to the high speed hip flexion / knee extension movements. The eccentric work demands at these tasks are huge and any change on its ideal function and structure can put athletes at real risk.
This contribution from Schuermans J, et al. relates to agonists high load recruitment impairment.
The authors have found a special metabolic recruitment activation pattern within hamstring muscles under a fatiguing high threshold task.
They have scanned 54 football players from a control group (1) and a history of hamstring injury group (2 - injury related) just after a task of prone leg curling to exhaustion.
The control group presented with more recruitment variability while the injury related group had a more balanced pattern.
"More symmetrical muscle activation (lower level of intramuscular dissociation) might imply compensatory and (mal)adaptive neuromuscular coordination patterns, causing the hamstring muscle bellies to contract less efficiently, with earlier onset of pH changes and muscle fatigue."
The authors hypothesis, supported by the control group findings, "suggests that under high loading conditions, the semitendinous (ST) has a prominent role in producing and controlling torques around both hip and knee joints."
One of the interesting results from the injury related group is that part of the recruitment balance was related to a decreased in the activity share from ST. A deficit in ST probably overloads biceps femurs (BF) on its attempt to keep function.
So, thinking about bringing all of this into daily practice, what does a deficit in ST and overload of BF during high load tasks can means in terms of uncontrolled movement site and direction?
A high threshold tibial external rotation uncontrolled movement can be a possible finding?
And what about retraining strategies? A bridge hamstring curl with knees together could be a starting point at helping recover ST prominent high load function? Which other strategies would you use? And how would you know the chosen one is the best for each case?
Movement related injury risk can came from different regions in the kinetic chain. A systematic and practical screening tool can well fill your needs on the daily practice of a movement health work.
Think about this! #thinkmovement
Biceps femoris and semitendinous - teammates or competitors? New insights into hamstring injury mechanisms in male football players: a muscle functional MRI study
Schuermans J, et al. Br J Sports Med 2014;48:1599–1606. doi:10.1136/bjsports-2014-094017
The hamstring injury mechanism was assessed by investigating the exercise-related metabolic activity characteristics of the hamstring muscles using a muscle functional MRI (mfMRI) protocol.
27 healthy male football players and 27 football players with a history of hamstring injuries (recovered and playing fully) underwent standardised mfMR Imaging. The mfMRI protocol consisted of a resting scan, a strenuous bilateral eccentric hamstring exercise and a post exercise scan. The exercise-related T2 increase or the signal intensity shift between both scans was used to detect differences in metabolic activation characteristics (1) between the different hamstring muscle bellies and (2) between the injury group and the control group.
A more symmetrical muscle recruitment pattern corresponding to a less economic hamstring muscle activation was demonstrated in the formerly injured group (p<0.05). The injured group also demonstrated a significantly lower strength endurance capacity during the eccentric hamstring exercise.
Conclusions These findings suggest that the vulnerability of the hamstring muscles to football-related injury is related to the complexity and close coherence in the synergistic muscle recruitment of the biceps femoris and the semitendinosus. Discrete differences in neuromuscular coordination and activity distribution, with the biceps femoris partly having to compensate for the lack of endurance capacity of the semitendinosus, probably increase the hamstring injury risk.
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