Pressure Applied during Deep Friction Massage: Characterization and Relationship with Time of Onset of Analgesia

This study aims to determine if a dose–response relationship exists between the pressure applied during deep friction massage (DFM) and the time to the onset of analgesia in an asymptomatic patellar tendon. For this purpose, pressures applied by physiotherapists during DFM (study 1) were characterized and then, based on these pressures, the effects of different DFM pressures on the time to the onset of analgesia were assessed (study 2). First, the mean pressure applied by 40 physiotherapists during a DFM session was assessed with a pressure sensor through an observational, cross-sectional and analytical study. Next, the effects of different pressure intensities (the median, the percentile 25 (P25), and the percentile 75 (P75) of the mean pressure obtained in study 1) were studied in a crossover trial enrolling 30 participants with an asymptomatic patellar tendon. A pressure sensor was used to register the pressures applied during DFM. Our main results indicated that the physiotherapists applied pressures with a wide variation ((mean pressure: 2.317 kg/cm2 (P25: 1.022 kg/cm2; P75: 4.161 kg/cm2)). It was also shown that higher pressures had shorter times to the onset of analgesia (pressure: 1 kg/m2, time to the onset of analgesia: 67.0 s (P25: 84.5 s; P75: 113.5 s); pressure: 2.3 kg/m2, time to the onset of analgesia: 59.0 s (P25: 73.5 s; P75: 87.3 s); pressure: 4.2 kg/m2, time to the onset of analgesia: 37.8 s (P25: 54.0 s; P75: 62.0 s)) (p ≤ 0.001). In conclusion, the mean DFM pressure obtained by the physiotherapists was 2.3 kg/cm2 (P25: 1.02 kg/cm2; P75: 4.16 kg/cm2). Higher pressures of DFM resulted in shorter times to the onset of analgesia.