## 4 Discussion
In this regard, our results also suggest that patients with chronic AKP may achieve therapeutic effects by performing ten sessions over 3.5 weeks of the DAPRE technique-based strengthening exercises alone. Our patients could have adapted to performing exercise training by repetitive muscle contractions over ten sessions, which possibly increased joint stability and movement efficiency, resulting in gradual pain reduction [35]. Since RTD is the ability for rapid muscular force exertion [37], an improvement in quadriceps RTD (20%, ES = 0.62) might lead to increased knee joint power in the sagittal plane [38]. Additionally, 95% confidence intervals for quadriceps PT (13%, ES = 0.90) do not contain zeros, suggesting that an improvement in quadriceps endurance is clinically meaningful. Therefore, observations of increased quadriceps power and endurance at post-rehabilitation also support the idea that the conduct of resistance exercises with functional movements (particularly squats and lunges) could have made daily activities easier. This could have been associated with significant reductions in pain during ADL and at the worst pain level, which could explain why lower-extremity functional outcomes showed a further improvement after the 4-week detraining period. Although between-group differences were determined in LEFS score, the associated 95% confidence intervals do not contain zero in the condition of modality + exercise (Figure 3), an advantage of electro-cryotherapy in promoting functional improvements may exist. Looking at the LEFS scores, those of patients who received electro-cryotherapy increased by almost 10 points (ES = 0.87), whereas those of patients who performed exercise only increased 4 points (ES = 0.36). A LEFS score of 9 points is known as the minimal clinically important difference [20] where we still recommend applying electro-cryotherapy in every session during rehabilitation exercise for AKP patients. Interestingly, the effect sizes calculated in the condition of modality + exercise are consistently larger than those in exercise alone after rehabilitation and even grew larger in a comparison of pre-rehabilitation and detraining (cm in VAS during ADL: 2.6 versus 1.7; at worst: 3.1 versus 1.6; LEFS: 1.4 versus 0.9). As previously reported, concerning the effect of TENS and cryotherapy in reducing residual pain after therapeutic exercises [35], patients received electro-cryotherapy in our study may have been likely to go home in better physical (or psychological) condition during and after the rehabilitation program. The application of study outcomes to the pathological population may be a limitation because 20% (7/35) of our patients had a history of knee surgeries (ACL reconstruction: \(n\) = 2, posterior cruciate ligament reconstruction: \(n\) = 1, meniscal surgery: \(n\) = 2, ACL reconstruction and meniscal surgery: \(n\) = 2). However, quadriceps (MVIC: 2.3 versus 2.7 Nm/kg; CAR: 0.8 versus 0.8) and self-reported functions (VAS during ADL: 3.6 versus 4.1 cm; LEFS: 50 versus 53 points) at the beginning of rehabilitation in patients with surgical history were not different from those who did not have surgeries. Additionally, those patients with surgical history were somewhat evenly allocated (3 and 4 in each treatment condition), which could have also minimized the heterogeneity of patient characteristics. The average rehabilitation period of our patients was 24 days. We assume that further improvements (e.g., muscle hypertrophy) beyond what we observed could be expected if patients would participate in additional exercise training. Ten sessions, however, was the maximum number that we asked our patients to attend due to rehabilitation adherence and detraining.