Elite Sport Services

New diagnostic method
for prediction of hamstring injures
Carmelo Bosco Ph. D., D. U., D. Hon .C.

Hamstring strains are among the most common injuries (and re-injuries) in athletes. Hamstring muscle tear takes place during eccentric exercise when the muscle develops tension while lengthening. To determine the relation of hamstring and quadriceps muscle strength and imbalance to hamstring injury isokinetic, strength test usually has been utilised (57). It is generally thought that to prevent hamstring injures, the H/Q ratio assessed with isokinetic device, should not be less than 60 %. Unfortunately this is only a poor evaluation to predict possible hamstring injures. In fact the strength assessment performed with constant speed device operated at low speed (3-4 rad/s) cannot be compared with the force developed during eccentric work at extremely high speed (14). In this connection it has been noted that isokinetic strength testing does not predict hamstring injury in athletes (4).

In light of the above observations it was introduced a new functional test which allow to assess the leg extensor muscle functions during ballistic motion like vertical jump. During a vertical jump performed from half squat position, hamstring and quadriceps co-contraction has been documented and explained via a co-contraction hypothesis. This hypothesis provide a stabilising force at the knee by producing a posteriorly-directed force on the tibia to counteract the anterior tibial force imparted by quadriceps. EMGrms was recorded from right and left hamstring (HR, HL) and left rectus femoris (RFL) in order to determine muscle recruitment patterns of knee extensor and flexor. In fig. 14 are presented an example of a female sprinter, revealing the both RFL and HL were strongly engaged during vertical push off while the HR demonstrated only moderate activity at the end of the push off. The high activity noted in the HL was associated with a previously hamstring injury.

On the other handthe HR showed low level of activity. This is reflecting the low demand placed on the hamstring muscle to counter anterior shear force acting at the proximal tibia. These altered neural strategies reflect changes in neural inputs to the motoneuron pools that will be recruited in generation a specific motor task. To try to detect possible dysfunction it was compared the EMGrms activity of Q with H. Preliminary results revealed that when the EMGrms ratio Q/H is more than 1, no problems could be noted in the hamstring. On the other hand if the ratio was lower than 1, some symptom of hamstring injury was claimed by the athletes. Similar procedure have been suggested recently to assess muscle dysfunction (26)

Fig. 14. Electromyogram root-mean square (EMGrms) recorded in the hamstring left (HL)and right (HR) and rectus femoris left (RFL) from a female sprinter during vertical jumpperformance. In the figure is shown also the displacement in cm during the push of the jump. The high activation of the HL was connected to the claim of problems felt by the athlete inthe left hamstring.

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