Author(s): HRISCHEV, P., MANDADZHIEV, N., VASILEV, V., ANGELOVA, P., BOYADJIEV, N., GEORGIEVA, K. , Institution: MEDICAL UNIVERSITY - PLOVDIV, Country: BULGARIA, Abstract-ID: 1894

INTRODUCTION:
Muscle balance of the thigh is commonly tested with isokinetic dynamometers, which allows the calculation of the hamstring/quadriceps (H/Q) ratio. This metric is typically associated with the risk for non-contact injuries in the thigh and knee areas. Traditional testing is done in a rested setting with slow isokinetic speeds where the athlete can develop maximal force. These types of injuries, however, are heavily correlated to the accumulation of fatigue in certain sports, which require high speed muscle contractions. We devised an isokinetic protocol reflecting these specific characteristics, with the aim to test how muscle balance changes during and after fatigue.
METHODS:
The study included 7, recreationally active at the time of investigation, male participants (age:23.43+/-1.27 years, height:181.4+/-4.54 cm, weight:87.84+/-11.11 kg, body fat percentage:15.69+/-1.79 %, BMI:26.64+/-2.78). Isokinetic strength assessment of knee flexion and extension was done using a HUMAC NORM isokinetic dynamometer (Computer Sports Medicine Inc., Stoughton, Massachusetts, USA). The contraction modes used were concentric and eccentric at a set speed of 60 deg/sec and 300 deg/sec. The slow speed test consisted of 5 maximal repetitions, while the fast speed fatigue test consisted of 50 repetitions of maximal eccentric knee flexions and concentric extensions.
RESULTS:
A paired samples t-test was performed to check for differences between the peak torque values of the dominant leg extensors, flexors and dynamic H/Q ratios at the two test speeds. The concentric extensor peak torque values at slow speeds (M=268 N/m; SD=54.36) were significantly higher than at fast speed (M=196.9 N/m; SD=86.76), t(6)=2.541, p=.044. On the contrary, eccentric flexor peak torque values were not significantly different at the slow (M=203.1 N/m, SD=66.64) and fast (M=166.4 N/m, SD=24.4) speeds. Dynamic H/Q ratios for the dominant leg at slow (M=0.756, SD=0.155) and fast (M=1.47, SD=0.796) speeds were borderline significantly different (t(6)= -2.338, p=.05) with higher H/Q ratios observed at fast speeds. Dynamic change in the H/Q ratios was also investigated through the duration of the fatigue test, by calculating the percentage change of the average H/Q values for the first 25 repetitions and the last 25 repetitions. Five of the subjects showed a decrease in H/Q ratio values of a mean 18.16%, while in two of the subjects, there was a mean increase of 48.92% in H/Q ratios after fatigue.
CONCLUSION:
As expected, high speed isokinetic testing renders lower peak torques for extensor knee musculature, while not changing flexor eccentric force, which leads to an increase in H/Q ratio values. This effect is even more amplified after fatigue when extensor muscles show less endurance capabilities, which leads to a further shift in muscle balance. Whether this can predict injury risk better than conventional testing, is yet to be investigated.