Patellar tendinopathy, often referred to as "jumper's knee," is a common overuse injury affecting the patellar tendon, particularly among athletes participating in sports involving frequent jumping, sprinting, or sudden directional changes such as basketball, volleyball, and football (1). It is characterized by localized anterior knee pain and tendon degeneration, which can significantly impair athletic performance and quality of life (2,3). The pathology is believed to result from repetitive mechanical loading that exceeds the tendon’s capacity for adaptation, leading to microtrauma and failed healing response (4).

Various conservative treatment strategies have been explored for patellar tendinopathy, among which exercise-based rehabilitation holds a central role (5). Eccentric training, involving controlled lengthening of the tendon under load, has gained substantial attention due to its proposed effects on collagen realignment, neovascularization reduction, and improved tendon stiffness (6,7). Several studies have demonstrated its efficacy in alleviating pain and restoring function in chronic tendinopathies (8,9).

On the other hand, concentric exercises, which focus on tendon shortening during contraction, have also been employed in rehabilitation protocols, although their physiological effects and clinical benefits in tendon healing remain less established (10,11). Some researchers suggest that concentric loading may be less effective in modifying tendon structure and promoting tissue remodeling when compared to eccentric loading (12).

Despite the widespread use of both modalities, limited data directly compare their outcomes in athletic populations with patellar tendinopathy. A comparative evaluation of eccentric versus concentric training can provide clearer insights into optimizing rehabilitation strategies. Therefore, this study aimed to assess the effectiveness of eccentric versus concentric exercise training on pain reduction and functional improvement in athletes diagnosed with patellar tendinopathy.

Study Design and Participants:

This randomized controlled trial was conducted over a period of 8 weeks at a tertiary-level sports rehabilitation center. A total of 60 athletes aged between 18 and 35 years, clinically diagnosed with chronic patellar tendinopathy (duration >6 weeks), were enrolled. Diagnosis was confirmed through clinical examination and ultrasound imaging. Participants with previous knee surgery, systemic musculoskeletal conditions, or recent corticosteroid injections were excluded.

Randomization and Group Allocation:

Participants were randomly assigned into two equal groups (n=30 each) using a computer-generated random sequence. Group A underwent an eccentric training program, while Group B performed concentric training exercises. All participants were informed about the nature and objectives of the study and provided written informed consent.

Intervention Protocols:

Both groups participated in supervised training sessions three times a week for six weeks.

• Eccentric Training (Group A): Participants performed single-leg decline squats on a 25° decline board, slowly lowering over 4 seconds, and returning passively to the start position using the opposite leg. Three sets of 15 repetitions were performed per session.
• Concentric Training (Group B): Participants performed single-leg squats on a flat surface, focusing on the upward phase of the movement. The downward phase was minimized in effort. The sets and repetitions matched those of the eccentric group.

Load progression was applied weekly by adding weights as tolerated. Both groups were instructed to avoid pain-provoking activities during the intervention period.

Outcome Measures:

Assessments were conducted at baseline, week 3, and week 6.

• Pain Intensity: Measured using the Visual Analog Scale (VAS), ranging from 0 (no pain) to 10 (worst pain).
• Functional Performance: Evaluated using the Victorian Institute of Sports Assessment–Patella (VISA-P) questionnaire, which assesses symptoms and sports function in patellar tendinopathy (score range: 0–100).

Statistical Analysis:

Data were analyzed using SPSS software (version 25.0). Within-group comparisons were performed using paired t-tests, while between-group differences were assessed using independent t-tests. A p-value of less than 0.05 was considered statistically significant.

A total of 60 athletes completed the study protocol without any dropout. Baseline demographic characteristics including age, sex, duration of symptoms, and baseline scores were comparable between the two groups (p>0.05).

Pain Intensity (VAS Scores):

Group A (eccentric training) showed a significant reduction in mean VAS scores from 7.2 ± 1.1 at baseline to 4.1 ± 0.8 at week 3 and 2.8 ± 0.9 at week 6. In contrast, Group B (concentric training) demonstrated a less pronounced decrease from 7.0 ± 1.0 to 5.3 ± 0.9 at week 3 and 4.5 ± 1.2 at week 6. The difference in pain reduction between groups at week 6 was statistically significant (p<0.01) (Table 1).

Functional Performance (VISA-P Scores):

In Group A, VISA-P scores improved from a baseline of 42.3 ± 6.4 to 66.5 ± 5.8 at week 3 and 82.6 ± 5.9 at week 6. Group B showed an increase from 43.1 ± 7.1 to 58.3 ± 6.1 at week 3 and 70.2 ± 6.7 at week 6. Between-group comparison revealed significantly greater functional improvement in Group A (p<0.01) (Table 2).

Table 1: Comparison of VAS Scores Between Groups A and B

Table 2: Comparison of VISA-P Scores Between Groups A and B

The statistical analysis confirms that eccentric training led to significantly greater improvements in both pain relief and functional ability compared to concentric training (Tables 1 and 2).

The present study aimed to evaluate and compare the effectiveness of eccentric and concentric training in the rehabilitation of athletes with chronic patellar tendinopathy. The findings demonstrated that eccentric training significantly improved both pain scores and functional outcomes over six weeks, compared to concentric training. These results align with previous literature supporting the superior benefits of eccentric loading for tendon rehabilitation.

Patellar tendinopathy is known to result from repetitive mechanical overload, leading to degeneration and disorganization of the tendon matrix rather than inflammation (1). Eccentric exercises are thought to stimulate tendon remodeling by inducing collagen synthesis, improving alignment, and promoting the resolution of neovascularization and nociceptive ingrowth (2,3). This is consistent with the significant pain reduction observed in the eccentric group in this study.

Alfredson et al. initially popularized the use of eccentric training for chronic tendinopathy, showing improved outcomes in Achilles tendon injuries (4). Subsequent trials extended these principles to patellar tendinopathy, with similar success (5,6). The use of a decline board, as applied in our protocol, has been shown to enhance tendon strain, which may further facilitate tendon adaptation (7). Young et al. also reported that eccentric decline squats produced greater improvements than traditional eccentric exercises in volleyball players (8).

In contrast, concentric exercises do not appear to elicit the same level of mechanical stimulus for tendon remodeling (9). Our results support this hypothesis, as the concentric group showed modest improvements in both VAS and VISA-P scores, but these were significantly lower than those in the eccentric group by week six.

Several mechanisms may explain the greater efficacy of eccentric training. These include increased tensile loading during muscle lengthening, which enhances mechanotransduction signaling pathways involved in tendon repair (10), as well as modulation of pain through alterations in cortical excitability and central sensitization (11). Additionally, eccentric training may induce positive neuromuscular adaptations such as improved muscle-tendon stiffness and motor unit recruitment (12,13).

Despite its benefits, compliance and tolerance to eccentric training can be challenging, especially during the early painful phases. However, none of the participants in this study discontinued due to discomfort, possibly due to proper supervision and gradual progression. This supports earlier findings that supervised eccentric protocols yield better adherence and outcomes (14).

Our findings are also in agreement with the systematic review by Kongsgaard et al., who reported that eccentric training was superior to other modalities, including concentric, isometric, and pharmacological treatments (15). While concentric training may still have a role in general strengthening and return-to-sport preparation, it appears to be less effective in reversing the degenerative pathology characteristic of tendinopathy.

Limitations
The study was limited by its relatively short follow-up period and the exclusion of imaging follow-up to assess tendon structural changes. Future studies with long-term follow-up and incorporation of imaging or biomechanical assessments may provide deeper insights.

Eccentric training demonstrated superior improvements in pain and functional outcomes compared to concentric training in athletes with patellar tendinopathy. It should be considered the preferred approach in rehabilitation protocols aimed at tendon recovery in sports populations.

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