The researcher apply a study aim to recognize some isokinetic characteristics and variables related to EMG of some lower limb muscles resbonsible for joint activity (right and left) for free and fin swimmer, the researcher used the descriptive method as its is appropriate for the research nature, the sample was chosen intentionally, they were two player free junior swimmer  acquire regional championship and the other is a fin junior swimmer achieve the African championship (under 13 year). In chosing the player it was taken into consideration that both of them is in a higher training state ready to an international external championship. Research results related to siokinetic measurements shows that  there is an increase in percentage of extension average work value, total extension work, flexion average power, extension average power, range of motion for left side ankle joint performance in attribute to right side (T₁/T₂) for fin swimmer higher than free swimmer, also there was an increase in the same percentage for left side ankle joint performance in attribute to right side (T₂/T₁) for free swimmer higher than fin swimmer, increase in percentage of flexion average work, and total flexion work for left side ankle joint performance in attribute to right side (T₁/T₂) only to free swimmer higher than fin swimmer , also there was an increase in the same percentage for left side ankle joint performance in attribute to right side (T₂/T₁) for fin swimmer higher than free swimmer,  also amount of working muscles endurance and joint range of motion, and producing resistance equal to performance power of the player inside water for planter flexion and Dorsi flextion to perform a complete ankle joint movement which allow floating and doesn't disturb the horizontal position and participation of muscular work in a way allow overcoming different resistance for free and fin swimmer.           Results related to EMG measurement shows that some lower limb muscles (right and left) participated in isokinetic performance of ankle joint for free and fin  swimmer has a variation and closeness in EMG measurement for median frequency (MF), value of EMG average (AEMG), as for measurement of mean power frequency (MPF) value doesn't differ too much. The results of sharing rate of work for both limbs muscles (Gastrocnemius muscle –lateral part, Gastrocnemius muscle – medial part, Tibials anterior muscle) work  almost with the same rate, closeness in measurement results of area exerted work amount for (Rectus femoris, vastus lateral is muscle, vastus medialis muscle, semitendinosus muscle, Biceps femoris muscle ) and an increase in (Gastrocnemius muscle – lateral part, Gastrocnemius muscle – medial part, Tibials anterior muscle), results of total area exerted work record for free swimmer