The purpose of this study is to determine whether active stretching with low frequency currents are more effective than active stretching in the treatment of hamstring shortness syndrome in children.

In 2012 we studied 51 young footballers with Short Hamstring Syndrome in Spain. Three groups were formed:

1. Stretching+Transcutaneous Electrical Nervous Stimulation (TENS);
2. Active stretching;
3. Conventional stretching.

Parameters: straight leg raise test (SLR), popliteal angle with the passive knee extension test (PKE) and the toe-touch test (TT).

The inter-group means were compared and clinically relevant parameters calculated [relative risk (RR), absolute risk reduction (ARR), relative risk reduction (RRR) and number needed to treat (NNT)].

Inclusion Criteria:

• children between 10 to 16.
• children federated belonging to Football School of Jumilla.
• children whose result in the assessment of range of motion is less than 70º in the Straight Leg Raising Test.
• not afraid to present the application of electrotherapy.
• not have low back pain in last three months.
• not to be injured

Exclusion Criteria:

• children who have acute muscle injury or ligamentous.
• children with recent fractures or unconsolidated.
• children with ligamentous laxity.
• functional shortening suffering children