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Can adding strength training to an endurance training program improve maximal oxygen consumption (VO2max) in cyclists? A systematic review and meta-analysisSeptember 26, 2022
Michael Rosenblat, PT, PhD, CEPABSTRACTThe objective of this review was to determine if concurrent strength and endurance training will lead to greater improvements in VO2max compared to endurance training alone in cyclists. Studies were included in the systematic review if they met the following criteria: 1. peer reviewed, academic journals, 2. published in the English language, 3. controlled trials, 4. included cyclists, 5. included a concurrent training intervention group, 6. included an endurance only training control group, and 7. included VO2max. Two databases, Medline (Ovid) and SPORTDiscus (EBSCOhost), were used to conduct an electronic search including all publication years (i.e., from inception) up to and including September 11, 2022. A total of 12 full-text articles were retrieved. Eight articles were included in the quantitative analysis. Three of the studies did not randomize participants into their respective groups. There was a total of 139 (male and female) participants. The mean age and VO2max ranged from 19 to 36 years and 48 to 78 ml×kg-1×min-1. The pooled analysis indicated that there was no statistically significant difference in VO2max between concurrent training and endurance only training (MD = -0.40 ml×kg-1×min-1, 95% CI = -2.03 to 1.23, p = 0.6310). Concurrent strength and endurance training does not produce a greater increase in VO2max compared to endurance only training in cyclists.
1 INTRODUCTION1.1 BackgroundConcurrent training involves the inclusion of both strength training and endurance training in a single training program to enhance performance.
Maximal oxygen consumption (VO2max) is considered to be the highest rate that oxygen can be consumed, transported and utilized by an individual [1]. It is defined by a plateau in oxygen uptake, which is indicated by an increase of less than 150 mL×min-1 following an increase in workload. A second measurement that can indicate that an individual has reached their VO2max is a respiratory exchange ratio (RER) of greater than 1.15 [2]. In the case where these physiological values are not reached between the last two stages of work, the test results represent peak oxygen consumption (VO2peak) [3]. 1.2 ObjectiveTo determine if concurrent strength and endurance training will lead to greater improvements in VO2max compared to endurance training alone in cyclists.
2 METHODSThe Cochrane Handbook for Systematic Reviews of Interventions was used to develop our methodology [4]. The findings were reported as per the 2020 PRISMA statement [5] with guidance from the PERSiST elaboration guidelines for systematic reviews in exercise science [6].
2.1 Eligibility CriteriaStudies were included in the systematic review if they met the following criteria: 1. peer reviewed, academic journals, 2. published in the English language, 3. controlled trials, 4. included cyclists, 5. included a concurrent training intervention group, 6. included an endurance only training control group, and 7. included VO2max.
Studies were be excluded for the following reasons: 1. the full text article is unavailable, 2. participants had pathology, 3. the study contained nutritional interventions (supplements, hydration, fed state, etc.), 6. participants were subject to changes in environmental conditions (heat, cold, altitude, hypoxia, hyperoxia, etc.), 7. inclusion of other modalities (cryotherapy, etc.), 8. included pharmacological agents, and 9. the study did not include group means with accompanied standard deviation (SD) or standard error of the mean (SEM) for the primary outcome. 2.2 Information SourcesTwo databases, Medline (Ovid) and SPORTDiscus (EBSCOhost), were used to conduct an electronic search including all publication years (i.e., from inception) up to and including September 11, 2022.
2.3 Search strategyThe search strategy follows a PICOS style approach, excluding study design to ensure that a broad and inclusive search will be conducted. The search strategy included a list of synonyms and tenses for relevant interventions and outcomes. The search limits were set to the following: titles, abstracts, English language, and academic journal articles. Below are the search terms.
2.3.1 Search Terms(cycling OR cyclist OR cyclists OR cycle OR cycler OR cyclers OR bicycle OR bicyclist OR bicyclists OR biking OR bike OR biker OR bikers)
(strength exercise OR strength training OR resistance exercise OR resistance training OR explosive exercise OR explosive training OR circuit exercise OR circuit training OR functional exercise OR functional training OR weight training OR weight exercise OR concurrent training OR concurrent exercise OR plyometrics OR plyometric training OR plyometric exercise) (endurance training OR endurance exercise OR aerobic training OR aerobic exercise) Ovid: (concurrent adj5 training) EBSCOhost: (concurrent N5 training) (maximal oxygen consumption OR maximal oxygen uptake OR maximum oxygen consumption OR peak oxygen consumption OR peak oxygen uptake OR aerobic power OR vo2max OR vo2peak) 2.4 Selection ProcessA single reviewer independently completed two levels of article screening (1. title and abstract, and 2. full-text) and abstracted data from the full-text articles.
2.5 Data Collection ProcessOne reviewer independently extracted the data from each of the studies. When multiple studies report data from the same study population, the publication with the earliest date was considered the primary publication. Whenever possible, Plot Digitizer (https://plotdigitizer.com) was used to extract data from figures that was not otherwise available in the text or tables of the respective articles.
2.6 Data ItemsData for the following categories were extracted: study design, participant baseline data (means, SD, and/or SEM), intervention and comparator characteristics, and outcome details were extracted.
2.7 Study Risk of Bias AssessmentCochrane Collaboration Risk of Bias 2.0 Tool was used to determine the level of bias in intervention studies [7]. One reviewer independently assessed the individual articles.
2.8 Effect MeasuresThe primary outcome assessed in the review was the mean difference in VO2max between the concurrent training and endurance only training groups. VO2max is a continuous variable and was expressed in ml×kg-1×min-1.
2.9 Synthesis MethodsData synthesis was performed for the mean difference (MD) in VO2max (ml×kg-1×min-1) between the concurrent training and endurance only training groups.
Data conversions were performed to determine values for missing data as well as to standardize scores to allow for a consistent interpretation of the results. Data expressed using the standard error of the mean (SEM) were converted to a standard deviation (SD) using the following formula: ; where n represents the sample size of the group. The mean difference for TT was pooled using the metafor package (version 2.4-0) in R (version 4.0.2) using a random effects model and the DerSimonian-Laird estimator. The I2 statistic was used to describe the degree of statistical heterogeneity by determining the percentage of the total variation in the estimated effect across studies. I2 values of 25%, 50%, and 75% were considered as low, moderate, and high degrees of statistical heterogeneity [8]. 2.10 Reporting Bias AssessmentThe relationship between the effect size and the sample size was determined visually using a funnel plot. Egger’s test was used to quantitatively assess for small sample size bias [9].
3 RESULTS3.1 Study SelectionA total of 302 records were identified by searching Medline (Ovid) and SPORTDiscus (EBSCOhost). See Figure 1 (click here). After removing duplicates and screening titles and abstracts a total of 12 full-text articles were retrieved. Eight articles were included in the quantitative analysis. See Table 1 (click here).
3.2 Study CharacteristicsThree of the studies did not randomize participants into their respective groups [10-12]. There was a total of 139 (male and female) participants. See Table 2 (click here). The mean age and VO2max ranged from 19 to 36 years and 48 to 78 ml×kg-1×min-1. The concurrent training and endurance only training groups performed the same endurance programs. The resistance training programs for the concurrent training groups can be found in Table 2 (click here).
3.3 Risk of Bias in StudiesThe overall risk of bias was high for 4 of the 8 studies. The results of the risk of bias analysis can be found in Figure 2 (click here).
3.4 Results of Individuals StudiesThe results of the individual studies can be found in Table 3 (click here).
3.5 Results of SynthesesThe pooled analysis indicated that there was no statistically significant difference in VO2max between concurrent training and endurance only training (MD = -0.40 ml×kg-1×min-1, 95% CI = -2.03 to 1.23, p = 0.6310). See Figure 3 (click here). Furthermore, there was no evidence of statistical heterogeneity (I2 = 0%).
3.6 Reporting BiasThere was no indication of small sample size bias following visual inspection of the funnel plot or from the results of Egger’s test for funnel plot asymmetry (beta = 1.73, 95% CI = -2.06 to 5.53, z = -1.2188, p = 0.2229). See Figure 4 (click here).
4 DISCUSSION4.1 Limitations4.1.1 Evidence Included in the Review
4.1.2 Review Process
5 CONCLUSIONConcurrent strength and endurance training does not produce a greater increase in VO2max compared to endurance only training in cyclists.
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