High Frequency RF Current Effects on Muscle Pain and Function

Individuals with Muscle Injury Inclusion Criteria: * Age over 18 years. * Athletes: amateur soccer players or sprinters with regular, systematic training. * Suspected Grade I or II hamstring strain. * Cessation of training due to injury. * No surgical intervention in the previous year (for initial assessment as potential participants). Exclusion Criteria: * History of injury to the same muscle (ipsilateral side) within the last 6 months. * Other injury to the posterior aspect of the thigh. * Other injuries or chronic pain in the trunk or lower limbs. * Use of non-steroidal anti-inflammatory drugs (NSAIDs) in the 3 months prior to the injury. Individuals with Acute Low Back Pain Inclusion Criteria: * Age over 18 years. * Pain located between the lower ribs and the gluteal folds (top of the buttocks). * Pain occurred on fewer than half of the days over the preceding six months. * Pain intensity $\\ge$ 6/10 on the Visual Analogue Scale (VAS). * Pain related to one or more of the following: * Lumbar facet joints * Sacroiliac joints * Lumbar intervertebral discs * Muscles, tendons, or ligaments of the lumbar and sacral region * Other bony structures of the lumbar spine * Discontinuation of non-steroidal anti-inflammatory drugs (NSAIDs) or analgesics: * 1 day prior to measurement * 48 hours after measurement Exclusion Criteria: * Radiographic evidence of inflammatory disease affecting the spine. * Spinal fracture. * Significant genetic structural abnormality of the spine. * Pregnancy. * Psychiatric disorders. * Receipt of systemic medication or treatment in the last 3 months. * Presence of neurological deficits (sensory, motor, or reflexes). * Receipt of TENS or TECAR therapy within the last year. Individuals with Chronic Low Back Pain Inclusion Criteria: * Episodes of low back pain (between the lower rib margin and the gluteal fold) for at least half of the days during the last 6 months. * Pain intensity $\\ge$ 20% on the Visual Analogue Scale (VAS). Exclusion Criteria: * Spinal stenosis. * Radiographic evidence of inflammatory disease affecting the spine. * Vertebral fracture. * Presence of spondylolisthesis or spondylolytic lesion (spondylolysis). * Significant genetic structural abnormality of the spine. * Daily, severe low back pain. * Pregnancy. * Use of medications that might influence heart rate or blood pressure. * Psychiatric disorders.