Re: Effects of resistance training with/without photobiomodulation on muscle and respiratory function in difficult-to-control asthma: a randomized trial

Abstract

This letter discusses Costa et al.’s randomized trial of resistance training (RT) combined with photobiomodulation therapy (PBMT) for difficult-to-control asthma (DTCA). The triple-blind study shows RT+PBMT safely improves peripheral muscle strength and exercise capacity better than RT alone. PBMT has dose-dependent effects, but optimal parameters for chronic respiratory patients remain unclear. Some clinicians have proposed standalone PBMT for DTCA patients unable to complete resistance training, but this approach has not been validated in clinical trials. The absence of a PBMT-only group limits assessment for patients unable to tolerate RT. The intervention did not improve lung function or asthma control, acting only peripherally. RT+PBMT is a useful adjuvant therapy; future studies should optimize PBMT dosing, test standalone PBMT, and examine long-term outcomes, and compare different PBMT wavelengths, energy settings and irradiation sites to refine real-world treatment protocols.

Dear Editor,

We read with great interest the randomized trial by Costa et al. investigating resistance training (RT) combined with LED-based photobiomodulation therapy (PBMT) in adults with difficult-to-control asthma (DTCA) [1]. This triple-blind, well-designed study demonstrates that RT+PBMT significantly improves peripheral muscle strength and functional exercise capacity compared with RT alone, with reliable safety. We commend the authors for addressing a key gap in pulmonary rehabilitation for DTCA.

While the original paper focuses primarily on reporting treatment efficacy, we aim to expand the discussion around the trial’s methodological limitations, practical challenges for clinical translation, and key directions for follow-up research. We hope these observations can offer useful insights for future study design and routine rehabilitation practice for chronic respiratory diseases.

Our comment centers on PBMT dosimetry and application protocol, which is critical for clinical translation. The authors used a fixed 850 nm LED regimen administered before each RT session [1]. While effective, PBMT effects are strongly dose-dependent, and optimal parameters for chronic respiratory patients remain undetermined. We searched PubMed and other major academic databases using keywords related to photobiomodulation, dose response and chronic respiratory disease, to review existing literature on PBMT dosing research in respiratory patient populations. Notably, we systematically searched PubMed and other major databases using the key terms ‘photobiomodulation’, ‘dose-dependent’, ‘chronic respiratory’ and found no published clinical studies specifically examining dose-dependent effects of PBMT in chronic respiratory populations. This gap matters greatly for patients such as those with DTCA. Most individuals with DTCA struggle with peripheral muscle weakness, poor exercise tolerance, and muscle damage linked to long-term glucocorticoid use, making them far more sensitive to external interventions than healthy people. Recent dosimetry research has confirmed PBMT follows a clear biphasic dose response: an incorrect dose will not only fail to deliver therapeutic effects, but may also place extra physical stress on vulnerable patients [2]. For this reason, developing reliable long-term dosing guidelines is critical to ensure safe, effective care for this patient group [3]. This underscores that the optimal long-term dosing parameters for patients with DTCA and similar conditions remain undetermined. Previous acute PBMT applications in asthma yielded null findings, likely due to single-session use rather than true ineffectiveness.

A notable design limitation is the lack of a PBMT-only group. Using PBMT as a standalone therapy to improve peripheral muscle function in severe DTCA patients who cannot participate in RT remains a theoretical idea only. Even so, existing research has shown PBMT can modulate muscle metabolism and enhance physical performance, which provides partial mechanistic support for this concept [4]. For patients with severe DTCA unable to tolerate RT, standalone PBMT could be a valuable option to alleviate peripheral muscle dysfunction. Meanwhile, the present intervention improved muscular and functional outcomes but not pulmonary function or asthma control, consistent with evidence that exercise and PBMT act peripherally without altering airway pathology. We also wish to discuss the potential of delivering PBMT to the thoracic region to relieve asthma symptoms. Chronic airway inflammation and increased bronchial reactivity are the core drivers of asthma. Mechanistically, thoracic PBMT can reduce local inflammation, improve microcirculation and regulate airway nerve activity, all of which may target asthma’s key pathological features [5]. At present, no randomized clinical trials have evaluated thoracic PBMT in DTCA patients. However, animal studies in chronic obstructive pulmonary disease (COPD) and allergic asthma models have proven low-energy chest light therapy can alleviate airway inflammation, reduce pro-inflammatory cytokines and improve local tissue perfusion [5, 6]. This application is still in early exploratory stages and requires formal clinical validation in human subjects [3]. Whether modified dosimetry or thoracic irradiation could add respiratory benefits deserves further study.

In summary, this trial strongly supports RT+PBMT as a safe, effective adjuvant strategy for DTCA. Future research should define optimal PBMT dosimetry, evaluate standalone PBMT, and assess long-term durability to enhance clinical applicability, alongside head-to-head comparisons of different PBMT wavelengths, energy densities and irradiation sites to improve clinical utility [7].

Author contributions

Ding Li and Qinsong Ye wrote the main manuscript text.

Funding

This research was funded by a grant from the Zhejiang Provincial Medical and Health Plan (2022KY1159, 2025KY1423, 2025KY1417 and 2025HY1019). Key Technology Breakthrough Program of ‘Ningbo Sci-Tech Innovation Yongjiang 2035‘(No.2024Z222). Ningbo Municipal Specialized Training Program for Young Technical Backbone Talents in Health (Yongweifa 2024-102-77). Ningbo High-Level Medical and Health Team Major Tackling Project and the Talent Development Program (2022020405). Ningbo Municipal Key Modern Medical Discipline Development Project(2026-A36).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.

Clinical trial number

Not applicable.