Threats to internal validity in exercise science: A review of overlooked confounding variables
Abstract
Internal validity refers to the degree of control exerted over potential confounding variables to reduce alternative explanations for the effects of various treatments. In exercise and sports-science research and routine testing, internal validity is commonly achieved by controlling variables such as exercise and warm-up protocols, prior training, nutritional intake before testing, ambient temperature, time of testing, hours of sleep, age, and gender. However, a number of other potential confounding variables often do not receive adequate attention in sports physiology and performance research. These confounding variables include instructions on how to perform the test, volume and frequency of verbal encouragement, knowledge of exercise endpoint, number and gender of observers in the room, influence of music played before and during testing, and the effects of mental fatigue on performance. In this review the authors discuss these variables in relation to common testing environments in exercise and sports science and present some recommendations with the goal of reducing possible threats to internal validity.
Integrity signals
Registry
Cites
Statistics
Claims the paper makes
Claims other papers make about this one
Each is checked against this paper’s own text: does it say what the citing paper says it does?
The 6-12 week time frame captures initial expansion of the ribosomal pool but does not clarify longer-term plateaus in ribosomal accretion, rates of ribosomal decay, or the biological ceiling of translational capacity.
“Although this time frame captures the initial expansion of the ribosomal pool, it does not clarify longer-term plateaus in ribosomal accretion, rates of ribosomal decay, or the actual biological ceiling of translational capacity that may be reached by elite athletes over years of training [141,216].”
From Ribosome Biogenesis as a Putative Bottleneck to Skeletal Muscle Hypertrophy: Mechanisms, Human Evidence, and Practical Modulators (2026) · cites this paper as [216]
Cites
Mental fatigue impairs physical performance in humans
Marcora, S., Staiano, W., & Manning, V. (2009) · Journal of Applied Physiology · doi:10.1152/japplphysiol.91324.2008 · Cited by 1,485 · see citing works
Gender differences in strength and muscle fiber characteristics
Miller, A. E. J., MacDougall, J. D., Tarnopolsky, M. A., & Sale, D. G. (1993) · European Journal of Applied Physiology and Occupational Physiology · doi:10.1007/bf00235103 · Cited by 1,094 · see citing works
Age-Associated Loss of Power and Strength in the Upper Extremities in Women and Men
Metter, E. J., Conwit, R., Tobin, J., & Fozard, J. L. (1997) · The Journals of Gerontology Series A: Biological Sciences and Medical Sciences · doi:10.1093/gerona/52a.5.b267 · Cited by 592 · see citing works
Enhancing the Learning of Sport Skills Through External-Focus Feedback
Wulf, G., Mcconnel, N., Gärtner, M., & Schwarz, A. (2002) · Journal of Motor Behavior · doi:10.1080/00222890209601939 · Cited by 435 · see citing works
Verbal encouragement: effects on maximum effort voluntary muscle: action
McNair, P. J., Depledge, J., Brettkelly, M., & Stanley, S. N. (1996) · British Journal of Sports Medicine · doi:10.1136/bjsm.30.3.243 · Cited by 358 · see citing works
The Effect of Training at a Specific Time of Day
Chtourou, H., & Souissi, N. (2012) · The Journal of Strength and Conditioning Research · doi:10.1519/jsc.0b013e31825770a7 · Cited by 329 · see citing works
Maximum Strength-Power-Performance Relationships in Collegiate Throwers
STONE, M. H., SANBORN, K., OʼBRYANT, H. S., HARTMAN, M., STONE, M. E., PROULX, C., WARD, B., & HRUBY, J. (2003) · Journal of Strength and Conditioning Research · doi:10.1519/00124278-200311000-00019 · Cited by 254 · see citing works
Marchant, D., Greig, M. P., & Scott, C. R. (2009) · The Journal of Strength and Conditioning Research · doi:10.1519/jsc.0b013e3181b8d1e5 · Cited by 246 · see citing works
Response inhibition impairs subsequent self-paced endurance performance
Pageaux, B., Lepers, R., Dietz, K. C., & Marcora, S. (2014) · European Journal of Applied Physiology · doi:10.1007/s00421-014-2838-5 · Cited by 243 · see citing works
The Effect of Manipulated Self-Efficacy on Perceived and Sustained Effort
Hutchinson, J. C., Sherman, T., Martinovic, N., & Tenenbaum, G. (2008) · Journal of Applied Sport Psychology · doi:10.1080/10413200802351151 · Cited by 215 · see citing works
The effects of frequency of encouragement on performance during maximal exercise testing
Andreacci, J. L., LeMura, L. M., Cohen, S. L., et al. (2002) · Journal of Sports Sciences · doi:10.1080/026404102753576125 · Cited by 205 · see citing works
The effects of synchronous music on 400-m sprint performance
Simpson, S. D., & Karageorghis, C. I. (2006) · Journal of Sports Sciences · doi:10.1080/02640410500432789 · Cited by 200 · see citing works
Attentional Focus on Suprapostural Tasks Affects Balance Learning
Wulf, G., Weigelt, M., Poulter, D. R., & McNevin, N. H. (2003) · The Quarterly Journal of Experimental Psychology Section A · doi:10.1080/02724980343000062 · Cited by 199 · see citing works
Exercise in the heat is limited by a critical internal temperature
Walters, T. J., Ryan, K. L., Tate, L. M., & Mason, P. A. (2000) · Journal of Applied Physiology · doi:10.1152/jappl.2000.89.2.799 · Cited by 181 · see citing works
SZMEDRA, L., & Bacharach, D. W. (1998) · International Journal of Sports Medicine · doi:10.1055/s-2007-971876 · Cited by 168 · see citing works
Increasing the Distance of an External Focus of Attention Enhances Standing Long Jump Performance
Porter, J. M., Anton, P. M., & Wu, W. (2011) · The Journal of Strength and Conditioning Research · doi:10.1519/jsc.0b013e31823f275c · Cited by 137 · see citing works
Effect of Attentional Focus Strategies on Peak Force and Performance in the Standing Long Jump
Wu, W., Porter, J. M., & Brown, L. E. (2011) · The Journal of Strength and Conditioning Research · doi:10.1519/jsc.0b013e318231ab61 · Cited by 126 · see citing works
Effects of music tempo upon submaximal cycling performance
Waterhouse, J. M., Hudson, P., & Edwards, B. (2009) · Scandinavian Journal of Medicine and Science in Sports · doi:10.1111/j.1600-0838.2009.00948.x · Cited by 124 · see citing works
Effects of Music on Work-Rate Distribution During a Cycling Time Trial
Atkinson, G., Wilson, D., & Eubank, M. R. (2004) · International Journal of Sports Medicine · doi:10.1055/s-2004-815715 · Cited by 124 · see citing works
Ginis, K. A. M., & Bray, S. R. (2009) · Psychology and Health · doi:10.1080/08870440903111696 · Cited by 117 · see citing works
Relationship Between Verbal Command Volume and Magnitude of Muscle Contraction
Johansson, C., Kent, B. E., & Shepard, K. F. (1983) · Physical Therapy · doi:10.1093/ptj/63.8.1260 · Cited by 115 · see citing works
Swart, J., Lamberts, R. P., Lambert, M., Gibson, A. S. C., Lambert, E. V., Skowno, J., & Noakes, T. D. (2008) · British Journal of Sports Medicine · doi:10.1136/bjsm.2008.055889 · Cited by 114 · see citing works
The effect of motivational music on sub‐maximal exercise
Elliott, D. L., Carr, S., & Orme, D. (2005) · European Journal of Sport Science · doi:10.1080/17461390500171310 · Cited by 102 · see citing works
Enhanced expectancies improve movement efficiency in runners
Stoate, I., Wulf, G., & Lewthwaite, R. (2012) · Journal of Sports Sciences · doi:10.1080/02640414.2012.671533 · Cited by 84 · see citing works
Effects of moderate and high glycemic index meals on metabolism and exercise performance
Kirwan, J. P., Cyr-Campbell, D., Campbell, W. W., Scheiber, J. F., & Evans, W. J. (2001) · Metabolism · doi:10.1053/meta.2001.24191 · Cited by 78 · see citing works
The influence of rhythm and personality in the endurance response to motivational asynchronous music
Crust, L., & Clough, P. (2005) · Journal of Sports Sciences · doi:10.1080/02640410500131514 · Cited by 75 · see citing works
Physiological and Psychological Effects of Deception on Pacing Strategy and Performance: A Review
Jones, H. S., Williams, E. L., Bridge, C. A., Marchant, D., Midgley, A. W., Micklewright, D. P., & McNaughton, L. R. (2013) · Sports Medicine · doi:10.1007/s40279-013-0094-1 · Cited by 65 · see citing works
Effects of Differentiated Music on Cycling Time Trial
Lim, H. B., Atkinson, G., Karageorghis, C. I., & Eubank, M. R. (2009) · International Journal of Sports Medicine · doi:10.1055/s-0028-1112140 · Cited by 55 · see citing works
The Effects of Self-Presentation on Perceived Exertion
Boutcher, S. H., Fleischer-Curtian, L. A., & Gines, S. D. (1988) · Journal of Sport and Exercise Psychology · doi:10.1123/jsep.10.3.270 · Cited by 46 · see citing works
Eston, R. G., Stansfield, R., Westoby, P., & Parfitt, G. (2012) · Psychophysiology · doi:10.1111/j.1469-8986.2011.01330.x · Cited by 45 · see citing works
Faulkner, J., Arnold, T., & Eston, R. G. (2010) · Scandinavian Journal of Medicine and Science in Sports · doi:10.1111/j.1600-0838.2010.01233.x · Cited by 43 · see citing works
Type of Encouragement Influences Peak Muscle Force in College-Age Women
Amagliani, R., Petrella, J. K., & Jung, A. (2010) · International journal of exercise science · doi:10.70252/yive7290 · Cited by 34 · see citing works
Binboğa, E., Tok, S., Çatıkkaş, F., GÜVEN, Ş., & Dane, Ş. (2013) · Journal of Sports Sciences · doi:10.1080/02640414.2012.758869 · Cited by 32 · see citing works
Startle Auditory Stimuli Enhance the Performance of Fast Dynamic Contractions
Fernández‐del‐Olmo, M., Río-Rodríguez, D., Iglesias‐Soler, E., et al. (2014) · PLoS ONE · doi:10.1371/journal.pone.0087805 · Cited by 29 · see citing works
Knowledge of the Endpoint: Effect on Perceptual Values
Coquart, J. B., & Garcin, M. (2008) · International Journal of Sports Medicine · doi:10.1055/s-2008-1038741 · Cited by 25 · see citing works
Focus of Attention for Strength and Conditioning Training
Makaruk, H., & Porter, J. M. (2014) · Strength and conditioning journal · doi:10.1519/ssc.0000000000000008 · Cited by 24 · see citing works
Williams, C. A., Bailey, S. D., & Mauger, A. R. (2011) · British Journal of Sports Medicine · doi:10.1136/bjsports-2011-090257 · Cited by 23 · see citing works
Silva, S. B., de Abreu, L. C., Valenti, V. E., et al. (2013) · International Archives of Medicine · doi:10.1186/1755-7682-6-38 · Cited by 14 · see citing works
Knowledge of repetitions range affects force production in trained females.
Halperin, I., Aboodarda, S. J., Basset, F. A., et al. (2014) · PubMed · Cited by 13 · see citing works
Self-citationPresence of Observers Increases One Repetition Maximum in College-age Males and Females
Baker, S., Jung, A., & Petrella, J. K. (2011) · International journal of exercise science · doi:10.70252/tbat4311 · Cited by 10 · see citing works
Lamarche, L., Gammage, K. L., & Gabriel, D. A. (2010) · The Journal of Strength and Conditioning Research · doi:10.1519/jsc.0b013e3181c1f7b3 · Cited by 10 · see citing works
Flagged first, then by citations
Cited by
Sorted by citations
No Benefit of Ingestion of a Ketone Monoester Supplement on 10-km Running Performance
EVANS, M., MCSWINEY, F. T., BRADY, A. J., & EGAN, B. (2019) · Medicine & Science in Sports & Exercise · doi:10.1249/mss.0000000000002065 · Cited by 82 · see citing works
Hartman, M. E., Ekkekakis, P., Dicks, N. D., & Pettitt, R. W. (2018) · Journal of Experimental Biology · doi:10.1242/jeb.186585 · Cited by 51 · see citing works
Lian, K., Hammarström, D., Hamarsland, H., Mølmen, K. S., Moen, S. C., & Ellefsen, S. (2024) · European Journal of Applied Physiology · doi:10.1007/s00421-024-05446-x · Cited by 3 · see citing works
Muñoz López, M., López-Gil, J. F., Ramírez de la piscina Viúdez, X., Baz-Valle, E., & Tornero Aguilera, J. F. (2026) · Cells · doi:10.3390/cells15111041 · Cited by 1 · see citing works
“Although this time frame captures the initial expansion of the ribosomal pool, it does not clarify longer-term plateaus in ribosomal accretion, rates of ribosomal decay, or the actual biological ceiling of translational capacity that may be reached by elite athletes over years of training [141,216].”
- Authors
- Halperin, I., Pyne, D. B., & Martin, D. T.
- Affiliations
- Edith Cowan University (AU)
- Corresponding author
- Halperin, Israel
- Venue
- International Journal of Sports Physiology and Performance
- Publisher
- Human Kinetics
- Published
- 2015-10
- Volume
- 10
- Issue
- 7
- Pages
- 823-829
- ISSN
- 1555-0265 (ISSN-L)
- 1555-0273
- OpenAlex
- W1995397610
- Cited by
- 89
- References
- 41
- Citations by year
- 2026: 8 · 2025: 9 · 2024: 13 · 2023: 14 · 2022: 7 · 2021: 2 · 2020: 11 · 2019: 6 · 2018: 9 · 2017: 5 · 2016: 3 · 2015: 2
- FWCI
- 6.51
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- International Journal of Sports Physiology and Performance (publishedVersion)
- PubMed (publishedVersion)
- Edith Cowan University Research Online (Edith Cowan University) (submittedVersion)
- University of Canberra Research Portal (submittedVersion)
- Topics
- Health Sciences › Medicine › Orthopedics and Sports Medicine › Sports Performance and Training
- Social Sciences › Psychology › Developmental and Educational Psychology › Sport Psychology and Performance
- Health Sciences › Medicine › Complementary and alternative medicine › Cardiovascular and exercise physiology
- Keywords
- internal validity, confounding variables, exercise testing, sports performance testing, test instructions, verbal encouragement, observer effect, music during exercise, mental fatigue
- MeSH terms
- Behavior Observation Techniques, Formative Feedback, Attention, Exercise Test, Mental Fatigue, Humans, Music, Research Design, Reproducibility of Results, Confounding Factors, Epidemiologic, Athletic Performance
About these checks
Registry, retraction, Cites and statistics results are computed, not judged, with one exception: a printed reference that no index lists is read once by a model before it counts as a citation error. Claims are extracted by a model and kept only when their quote appears verbatim in the text; each cited source is then checked, with a model’s help, for whether it says what the claim relies on. Those verdicts can be wrong — read the claim’s quote and the cited source before relying on one.
Statistics and arithmetic are recomputed, not judged.
Confidence bands are shown only for fields calibrated on our annotated test set. None is calibrated yet, so no band is shown.
What counts as a claim ›How we measure confidence ›How we check this ›
Are you an author, or do you see a problem with this page? Request a review