This study compared the acute effects of electrical energy transfer (TECAR) and transcutaneous electrical stimulation (TENS) on pain and flexibility after a hamstring injury. Young athletes received either a 20 ​min TECAR (n = ​24) or TENS (n ​= ​26) session within 5 days following a hamstring injury, while the control (CON, n ​= ​25) group was instructed to rest. Visual analogue scale (VAS), functional Assessment Scale for Acute Hamstring Injuries (FASH), straight leg raise test (SLR), and sit-and-reach scores (STR) were obtained prior to, immediately, 24, and 48 ​h after therapy. Group differences were detected after therapy in VAS and FASH scores (p ​< ​0.05). Compared to pre-therapy measurements, VAS scores showed a greater decrease in the TECAR group (−38.75% to −63.33%) than in the TENS group (−16.67% to −25.00%) and both were greater than in the CON group (−2.81% to −9.81%) (p ​< ​0.05). The TECAR group improved FASH scores (28.57%–48.21%) more than the TENS group (15.89%–27.79%) and both groups more than the CON group (0%–8.33%) (p ​< ​0.05). The increase in SLR and STR was greater in the TECAR group (6.26%–13.96%) than in the TENS (1.72%–9.53%) and CON groups (0%–3.03%). These results suggest that in the acute phase of hamstring injury, the use of TECAR and, to a lesser extent, TENS may relieve pain symptoms and bring some improvements in flexibility more than instructing patients to rest.