Sport Physiology

Sport Physiology

Differential Effects of Whey Protein Supplementation on Strength Across Various Muscle Groups in Adults: A Systematic Review and Meta-Analysis

Document Type : Review Article

Authors
Mahdi Zarreh 1
Fatemeh Kazeminasab 2
Ali Bahrami Kerchi 3
Fatemeh Sharafifard 4
Omid Zafarmand 5
1 Department of Physical Education and Sports Science, Faculty of Humanities, University of Kashan, Kashan, Iran.
2 Dpartment of Sports Physiology, Faculty of Sports Science, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran
3 Department of Sports Physiology, Faculty of Sports Sciences, Isfahan (Khorasgan) Branch, Islamic Azad University, Isfahan, Iran.
4 Dpartment of Physical Education and Sports Science, Faculty of Humanities, University of Kashan, Kashan, Iran
5 Dpartment of Physical Education and Sports Science, Faculty of Human Sciences, Yasouj University, Yasouj, Iran
10.22089/spj.2025.18220.2381
Abstract
Background and Purpuse
Skeletal muscle function is essential for performing daily tasks, maintaining independence, and preserving quality of life. Age-related neuromuscular decline, inactivity, and metabolic disorders contribute significantly to muscle atrophy and strength loss, increasing dependence and healthcare costs. Resistance training remains a fundamental strategy to counteract these effects, while nutritional supplementation, especially protein, has emerged as a synergistic aid. Among protein sources, whey protein—a rapidly absorbed dairy derivative rich in leucine—exerts potent stimulation of muscle protein synthesis through activation of the mTORC1 pathway. Its bioactive constituents, including lactoferrin and immunoglobulins, further support its widespread clinical and athletic use aimed at enhancing recovery and adaptive responses. Despite broad adoption, evidence on whey protein's efficacy in improving muscular strength across diverse adult populations is inconsistent. Some trials report marked gains, others minimal, confounding interpretation. This variance is linked to heterogeneity in training protocols (intensity, duration, exercise selection), participant factors (age, baseline strength, nutrition), and methodologies (dosing, strength assessments).Addressing these discrepancies, our systematic review and meta-analysis comprehensively evaluated whey protein's effects on adult muscle strength. It aimed to delineate strength response variances across movement patterns (e.g., compound lower-body exercises like squats versus isolated upper-body movements) while considering moderators including training intensity, supplementation protocol, and participant age. Synthesizing controlled trial data clarifies whey protein’s mechanistic action and practical efficacy. Findings indicate maximal benefits for lower-body compound movements combined with adequate resistance training, notably in older or protein-deficient individuals. These outcomes endorse whey supplementation as a strategic intervention against sarcopenia and functional decline, contingent on individualized application and movement specificity.
Methods
Adhering strictly to Cochrane and PRISMA guidelines, we executed exhaustive literature searches up to November 29, 2024, across PubMed, Scopus, and Web of Science, using curated search terms encompassing whey protein and various performance metrics. Supplementing electronic searches, manual Google Scholar and reference mining ensured comprehensive inclusion. Eligible studies were RCTs or non-randomized trials involving adults, reporting pre- and post-intervention muscle strength for targeted movements: biceps curl, chest press, knee and leg extension, squat, and isokinetic knee extension, with experimental arms receiving whey protein against controls. Exclusions involved animal studies, non-primary reports, crossover designs, and studies lacking relevant strength data.Extracted data detailed study design, demographics, training modalities, supplementation regimes (type, dose, timing), and strength outcomes (mean ± SD). Where necessary, numeric data were retrieved from graphical content using GetData software or through author correspondence. Methodological quality was assessed via a modified 9-item PEDro scale, excluding participant/instructor blinding criteria specific to exercise interventions. Scores ranged 0-9, with higher indicating superior quality.Random-effects statistical models generated weighted mean differences (WMDs) and 95% confidence intervals (CI). Heterogeneity was quantified by I² statistics, categorized as mild (<25%), low (25–50%), moderate (50–75%), or high (>75%). Publication bias assessment employed funnel plots and Egger’s regression, with p<0.10 indicating bias. Analyses utilized Comprehensive Meta-Analysis (CMA) software version 2.
Results
Whey protein supplementation significantly enhanced muscle strength in chest press (WMD = 3.914 kg; 95% CI: 0.784 to 7.045; P = 0.014), leg press (WMD = 9.118 kg; 95% CI: 2.187 to 16.048; P = 0.010), and squat (WMD = 7.657 kg; 95% CI: 5.324 to 9.990; P = 0.001) compared to controls. Conversely, no significant strength changes emerged for biceps curl (WMD = -0.992 kg; 95% CI: -2.538 to 4.521; P = 0.582), knee extension (WMD = 1.926 kg; 95% CI: -0.156 to 4.008; P = 0.070), or isokinetic knee extension (WMD = 3.786 kg; 95% CI: -1.748 to 9.319; P = 0.180).
Conclusion
Synthesizing findings from 20 studies, this meta-analysis confirms whey protein’s capacity to enhance muscular strength predominantly in multi-joint lower-body exercises, encompassing leg press, squat, with a trend toward knee extension improvement. A modest yet significant chest press strength increment was observed, while isolated upper-body strength measured by biceps curl showed no enhancement. Isokinetic strength gains were likewise non-significant. These outcomes suggest whey supplementation, particularly paired with resistance training, preferentially augments strength in complex lower-body movements. Its influence on upper-body musculature appears inconsistent and movement-specific. Hence, whey protein’s application should target lower-body strength optimization, notably for older individuals or those with inadequate protein intake. Further investigations are needed to elucidate molecular mechanisms underpinning these differential responses and refine protocols enhancing upper-body adaptation. Longitudinal, rigorously designed trials are imperative to establish comprehensive guidelines maximizing whey protein's ergogenic potential.

Article Message
This comprehensive analysis indicates whey protein effectively augments muscular strength in adults during lower-body multi-joint exercises like squats and leg presses, while evidence remains inconclusive regarding upper-body and isokinetic muscle performance. Variable responsiveness across muscle groups underscores the necessity for tailored supplementation strategies combined with targeted resistance training. Whey protein supplementation thus emerges as a valuable nutritional adjunct for enhancing muscular performance, with consideration for dosage, intervention duration, and individual training modalities.
Ethical Considerations
This systematic review is registered with the international Prospero database under code CRD420251157160.
Authors’ Contributions
All authors participated in all study phases including design, implementation, analysis, and manuscript preparation.
Conflict of Interest
The authors declare no conflict of interest.
Acknowledgments
Gratitude is extended to primary study authors who provided raw data contributing to this synthesis.


Keywords
Whey protein
Muscle strength
Adults
Nutritional supplement

Subjects

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END
Sport Physiology
Volume 17, Issue 67
Summer 2025
Pages 79-102

  • Receive Date 14 July 2025
  • Revise Date 07 October 2025
  • Accept Date 19 October 2025