Probiotic supplementation and performance during detraining and post-EIMD recovery in college volleyball players: exploratory RCT
Eight weeks of multi-strain probiotics showed a favorable direction of effect on isometric strength retention and post-exercise muscle damage markers in national-level college volleyball players, but the small sample and retrospective registration preclude confirmatory conclusions.
| Population | 28 national-level university volleyball players (National Level 1 or above; ≥6 years systematic training; 4 males and 10 females per group; aged 20 ± 1–2 years) |
|---|---|
| Intervention | Daily oral multi-strain probiotic for 8 weeks: Lactobacillus casei Zhang (≥8×10⁹ CFU) + Bifidobacterium lactis V9 (≥6×10⁹ CFU) + Lactobacillus plantarum P-8 (≥6×10⁹ CFU), 1 sachet post-breakfast |
| Comparator | Identical-appearing placebo (inert powder, 2 g/sachet) |
| Outcome | Maximal isometric strength (IMTP) after detraining; Isokinetic knee strength after detraining; Serum CK post-EIMD (24 and 48 h); Muscle soreness (DOMS) at 24 and 48 h post-EIMD; Squat jump height (SJ) and RFD post-EIMD; Vertical jump performance and sport-specific agility; Gut microbiota composition |
Summary of findings
| Outcome | Effect | 95% CI | Certainty | Clinical relevance | Notes |
|---|---|---|---|---|---|
| Maximal isometric strength (IMTP) after detraining | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Isokinetic knee strength after detraining | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Serum CK post-EIMD (24 and 48 h) | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Muscle soreness (DOMS) at 24 and 48 h post-EIMD | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Squat jump height (SJ) and RFD post-EIMD | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Vertical jump performance and sport-specific agility | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
| Gut microbiota composition | Not fully reported; in the IC 95% available in text | — | Low | — | 1 studies |
Context
Volleyball players perform approximately 200 jumps per match and face post-season detraining followed by abrupt return-to-training loads, creating conditions for explosive strength loss and exercise-induced muscle damage. The gut–muscle axis hypothesis posits that probiotics may modulate systemic inflammation and muscle energy metabolism. Nutritional interventions targeting this specific transition window remain scarce.
What the study showed
The probiotic group showed reduced decline or maintenance of isometric strength (IMTP) and isokinetic knee strength after the 2-week detraining period compared with placebo. Following the standardized 200 weighted-jump EIMD protocol, the probiotic group displayed lower serum CK elevations and lower DOMS at 24 and 48 h, with faster SJ height and RFD recovery. Complete absolute values with 95% CIs are not fully reported in the available text, preventing precise effect quantification. Gut microbiota data are reported as secondary outcomes without sufficient statistical detail in the available excerpt.
How it was done
Exploratory randomized, single-blind, placebo-controlled trial in 28 university volleyball athletes allocated 1:1 (n=14 per group) via computerized block randomization. Total duration 8 weeks (4-week regular training + 2-week taper/competition + 2-week detraining). EIMD protocol applied at week 8 (200 weighted vertical jumps); assessments at baseline (week 0), post-supplementation (week 8), immediately post-EIMD, 24 h and 48 h post-EIMD.
Effect magnitude
Effect sizes with 95% CIs are not fully reported across all outcomes in the available text; the trial is explicitly described as exploratory, meaning effect estimates are preliminary and insufficient for confirmatory inference.
Risk of bias
Very small sample (n=28, 14 per group) limits statistical power and precision of estimates. Retrospective trial registration (ChiCTR, after recruitment completed) and absence of prospective prespecification of primary outcomes and analysis plan raise risk of selective outcome reporting (assessable via RoB 2). Single-blind design (allocation staff aware of assignment) introduces performance bias risk. No strict dietary control beyond fermented food restriction. Two-week detraining period may not reflect real-world longer interruptions.
What this study does NOT prove
This study does not prove that multi-strain probiotics prevent detraining-related strength loss or accelerate post-EIMD recovery in volleyball athletes broadly; findings are not generalizable beyond Chinese national-level university athletes, and causality cannot be established from a single exploratory trial with n=28.
In clinical practice
Findings are insufficient to support routine clinical recommendation of multi-strain probiotics for strength maintenance during detraining in volleyball athletes. Clinicians and sports dietitians should await larger, adequately powered RCTs with prospective registration before adopting this intervention.
Limitations
Very small sample (n=28, 14 per group) limits statistical power and precision of estimates. Retrospective trial registration (ChiCTR, after recruitment completed) and absence of prospective prespecification of primary outcomes and analysis plan raise risk of selective outcome reporting (assessable via RoB 2). Single-blind design (allocation staff aware of assignment) introduces performance bias risk. No strict dietary control beyond fermented food restriction. Two-week detraining period may not reflect real-world longer interruptions.
What is still missing
RCTs with ≥60 participants per group, prospective registration, sex-stratified analyses, and variable detraining durations are required to confirm or refute findings from this pilot.
Technical appendix
Version history
- 1.0 · 2026-10-19 — Auto-generated under Evidence Standard v1.0