Interpreting Adaptation to Concurrent Compared with Single-Mode Exercise Training: Some Methodological Considerations

Optimizing Resistance Training for Sprint and Endurance Athletes: Balancing Positive and Negative Adaptations

Resistance training (RT) triggers diverse morphological and physiological adaptations that are broadly considered beneficial for performance enhancement as well as injury risk reduction. Some athletes and coaches therefore engage in, or prescribe, substantial amounts of RT under the assumption that continued increments in maximal strength capacity and/or muscle mass will lead to improved sports performance. In contrast, others employ minimal or no RT under the assumption that RT may impair endurance or sprint performances. However, the morphological and physiological adaptations by which RT might impair physical performance, the likelihood of these being evoked, and the training program specifications that might promote such impairments, remain largely undefined. Here, we discuss how selected adaptations to RT may enhance or impair speed and endurance performances while also addressing the RT program variables under which these adaptations are likely to occur. Specifically, we argue that while some myofibrillar (muscle) hypertrophy can be beneficial for increasing maximum strength, substantial hypertrophy can lead to macro- and microscopic adaptations such as increases in body (or limb) mass and internal moment arms that might, under some conditions, impair both sprint and endurance performances. Further, we discuss how changes in muscle architecture, fiber typology, microscopic muscle structure, and intra- and intermuscular coordination with RT may maximize speed at the expense of endurance, or maximize strength at the expense of speed. The beneficial effect of RT for sprint and endurance sports can be further improved by considering the adaptive trade-offs and practical implications discussed in this review.

The physical demands and physiological responses to CrossFit®: a scoping review with evidence gap map and meta-correlation

BACKGROUND

CrossFit® combines different types of activities (weightlifting, gymnastics, and cardiovascular training) that challenge aerobic and anaerobic pathways. Over the last few years, the scientific interest in CrossFit® has increased considerably. However, there have been no published reviews characterizing the physical demands and physiological responses to CrossFit®. The present study synthesizes current evidence on the physical demands and physiological responses to CrossFit®.

METHODS

The search was performed in three electronic databases (PubMed, Scopus, and Web of Science). Manuscripts related to the physical and physiological performance of adult CrossFit® participants written in English, Portuguese, and Spanish were retrieved for the analysis.

RESULTS

In addition, a meta-correlation was conducted to examine the predictors of CrossFit® performance. A total of 68 papers were included in the review. Physical and physiological markers differed between the different workouts analyzed. In addition, 48 to 72 h are needed to recover from a CrossFit® challenge. Specific tests that involve CrossFit® movements were more related to CrossFit® performance than non-specific.

CONCLUSION

Although the characterization of CrossFit® is dependent on the workout examined, the benefits of muscle hypertrophy are aligned with the recent findings of concurrent training. The characterization of CrossFit® entire sessions and appropriate recovery strategies should be considered in future studies to help coaches manipulate and adjust the training load.

Impact of Anaerobic Exercise Integrated Into Regular Training on Experienced Judo Athletes: Running Vs. Repetitive Throws

ABSTRACT

Kamandulis, S, Dudėnienė, L, Snieckus, A, Kniubaite, A, Mickevicius, M, Lukonaitiene, I, Venckunas, T, Stasiule, L, and Stasiulis, A. Impact of anaerobic exercise integrated into regular training on experienced judo athletes: running vs. repetitive throws. J Strength Cond Res 38(9): e489-e495, 2024-Anaerobic training in high-level athletes is of considerable interest to practitioners aiming to optimize performance. This study compared the impact of interval anaerobic training (IAT) sessions consisting of either high-intensity running or throwing that were performed twice a week together with regular judo training on the anaerobic and aerobic performance of experienced judo athletes. Employing a repeated-measures, counterbalancing, research design, 12 national team judo athletes (7 women and 5 men; mean age, 20.4 ± 0.95 years; mean judo training experience, 13.4 ± 1.4 years; competitive level, black belt first and second Dan) performed each IAT modality for 6 weeks, for a full training cycle of 12 weeks. Assessments of their anaerobic fitness (Cunningham and Faulkner Anaerobic Treadmill Test), sport-specific anaerobic fitness (Special Judo Fitness Test [SJFT]), and aerobic capacity (maximal incremental treadmill running test) were performed before, after 6 weeks, and after 12 weeks of training. The uphill running performance improved by 13.1% over the 12-week period ( p = 0.047). Simultaneously, there was a 9.0% improvement in the SJFT index and a 6.9% increase in the number of throws ( p = 0.011 and p = 0.017, respectively). Although a trend for throwing drills being more effective than interval sprint running was observed, the interaction effect lacked statistical significance ( p = 0.074). Moreover, no substantial changes were noted in aerobic endurance markers. In conclusion, this study suggests that incorporating specific and nonspecific high-intensity drills into a routine training regimen may enhance anaerobic capacity among well-trained judo athletes, potentially leading to favorable competitive outcomes.

Cardiorespiratory and aerobic demands of squat exercise

Squatting, a traditional resistance exercise classified as strength training, relies on anaerobic pathways, but its aerobic aspects remain unclear. We examined heart rate and oxygen demand during squats, exploring variations across different strength statuses. It fills gaps in understanding the cardiorespiratory effects of squatting, especially during multiple sets. Twenty-two young healthy resistance trained men (age: 28 ± 4 years) participated. Maximal oxygen consumption (V̇O2max) and 1 repetition maximum (RM) of squat were measured. Participants performed 5 sets of squat exercises at 65% of 1RM for 10 repetitions with 3-min rest intervals. Heart rate and pulmonary gas exchange were measured during the squat exercise. Participants were divided into high strength (HS; upper 50%) and low strength (LS; lower 50%) groups based on a median split of their 1 RM squat values (normalized to their body weight). During 5 sets of squat exercise, oxygen consumption (V̇O2) increased up to 47.8 ± 8.9 ml/kg/min, corresponding to 100.6% of predetermined V̇O2max. The HS group achieved a greater highest point of V̇O2 in relation to V̇O2max than the LS group (108.0 vs. 93.7%). During the exercise intervals, V̇O2 exceeded V̇CO2, while during the rest intervals, V̇CO2 surpassed V̇O2. Our findings suggest that the oxygen demand during squatting is notably substantial, which may vary according to the training status.

Solving the High-Intensity Multimodal Training Prescription Puzzle: A Systematic Mapping Review

BACKGROUND

High-Intensity Multimodal Training (HIMT) refers to all styles of high-intensity combined aerobic, resistance and/or bodyweight exercise. Previous heterogeneity in exercise prescription and reporting in HIMT reduces the understanding of which factors should be considered when prescribing HIMT (e.g., exercise volume, intensity, duration). Previous studies have demonstrated positive effects of HIMT on health and performance outcomes. However, methodological disparities limit comparisons between findings. The objective of this systematic mapping review was to examine which prescriptive considerations and health and performance outcomes have been reported on in HIMT. This review also examined the quantity and trends of research conducted on HIMT.

METHODS

A systematic literature search was conducted using Ovid Medline, SPORTDiscus and Cochrane Library databases and additional sources to identify studies up until February 2023. A total of 37,090 records were retrieved, of which 220 were included for review. 246 individual HIMT protocols were included for categorical analysis against the Consensus on Exercise Reporting Template (CERT) and Applied Research Model for the Sport Sciences (ARMSS).

RESULTS

A total of 85 unique terms were used to describe HIMT. Included studies most commonly prescribed HIMT using a consistent exercise selection and circuit format. Exercise intensity was inconsistently reported on and a large proportion of studies prescribed 'high-intensity' exercise at a level lower than the American College of Sports Medicine criteria for high-intensity (i.e., < 77% heart rate maximum). Participation location, supervision and participation format were the most commonly reported non-training variables. The most frequently reported outcomes were cardiovascular health, perceptual outcomes, body composition and biochemical outcomes. A large proportion of previous HIMT research was experimental in design.

CONCLUSIONS

Previous HIMT research demonstrates a lack of standardisation in reporting. Future studies should seek to follow guidelines (i.e., CERT) to improve reporting rigour. Additionally, forthcoming research should attempt to actively involve practitioners in implementation studies to improve ecological validity among interventions. Finally, future outcome measures should be accessible in practice and reflect common training goals of participants.

REGISTRATION

This review adhered to PRISMA-ScR guidelines.

PREREGISTRATION

osf.io/yknq4.

Perspectives on Concurrent Strength and Endurance Training in Healthy Adult Females: A Systematic Review

BACKGROUND

Both strength and endurance training are included in global exercise recommendations and are the main components of training programs for competitive sports. While an abundance of research has been published regarding concurrent strength and endurance training, only a small portion of this research has been conducted in females or has addressed their unique physiological circumstances (e.g., hormonal profiles related to menstrual cycle phase, menstrual dysfunction, and hormonal contraceptive use), which may influence training responses and adaptations.

OBJECTIVE

The aim was to complete a systematic review of the scientific literature regarding training adaptations following concurrent strength and endurance training in apparently healthy adult females.

METHODS

A systematic electronic search for articles was performed in July 2021 and again in December 2022 using PubMed and Medline. This review followed, where applicable, the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The quality of the included studies was assessed using a modified Downs and Black checklist. Inclusion criteria were (1) fully published peer-reviewed publications; (2) study published in English; (3) participants were healthy normal weight or overweight females of reproductive age (mean age between > 18 and < 50) or presented as a group (n > 5) in studies including both females and males and where female results were reported separately; (4) participants were randomly assigned to intervention groups, when warranted, and the study included measures of maximal strength and endurance performance; and (5) the duration of the intervention was ≥ 8 weeks to ensure a meaningful training duration.

RESULTS

Fourteen studies met the inclusion criteria (seven combined strength training with running, four with cycling, and three with rowing or cross-country skiing). These studies indicated that concurrent strength and endurance training generally increases parameters associated with strength and endurance performance in female participants, while several other health benefits such as, e.g., improved body composition and blood lipid profile were reported in individual studies. The presence of an "interference effect" in females could not be assessed from the included studies as this was not the focus of any included research and single-mode training groups were not always included alongside concurrent training groups. Importantly, the influence of concurrent training on fast-force production was limited, while the unique circumstances affecting females were not considered/reported in most studies. Overall study quality was low to moderate.

CONCLUSION

Concurrent strength and endurance training appears to be beneficial in increasing strength and endurance capacity in females; however, multiple research paradigms must be explored to better understand the influence of concurrent training modalities in females. Future research should explore the influence of concurrent strength and endurance training on fast-force production, the possible presence of an "interference effect" in athletic populations, and the influence of unique circumstances, such as hormone profile, on training responses and adaptations.

Network Meta-analysis of Combined Strength and Power Training for Countermovement Jump Height

Combined strength and power training in a training program is considered to improve the vertical jump, which is frequently quantified using the countermovement jump height. It is not yet clear whether one of the different training set structures, such as complex training, contrast training, compound training and traditional training, is superior to another. The aim of this review is to describe and assess the comparative effects of the set structures on countermovement jump height in healthy subjects. A systematic review and network meta-analysis (NMA) was conducted in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Network Meta-Analyses. Three databases were systematically searched. Risk of bias was assessed using the Risk of Bias 2 tool. NMAs were performed using a random-effects model. Twenty-four studies were included. All interventions were superior to control (no intervention) with mean differences ranging from 2.87 [95% confidence interval (CI): 1.99 to 3.74] for complex training to 3.43 (95% CI: 2.61 to 4.26) for traditional training. None of the training interventions were superior compared to each other in strength and/or power trained subjects, as well as in non-strength and/or power trained subjects. The findings support the combination of strength and power training to improve countermovement jump height.

Effects of Concurrent Resistance and Endurance Training Using Continuous or Intermittent Protocols on Muscle Hypertrophy: Systematic Review With Meta-Analysis

ABSTRACT

Monserdà-Vilaró, A, Balsalobre-Fernández, C, Hoffman, JR, Alix-Fages, C, and Jiménez, SL. Effects of concurrent resistance and endurance training using continuous or intermittent protocols on muscle hypertrophy: Systematic review with meta-analysis. J Strength Cond Res 37(3): 688-709, 2023-The purpose of this systematic review with meta-analysis was to explore the effects of concurrent resistance and endurance training (CT) incorporating continuous or intermittent endurance training (ET) on whole-muscle and type I and II muscle fiber hypertrophy compared with resistance training (RT) alone. Randomized and nonrandomized studies reporting changes in cross-sectional area at muscle fiber and whole-muscle levels after RT compared with CT were included. Searches for such studies were performed in Web of Science, PubMed, Scopus, SPORTDiscus, and CINAHL electronic databases. The data reported in the included studies were pooled in a random-effects meta-analysis of standardized mean differences (SMDs). Twenty-five studies were included. At the whole-muscle level, there were no significant differences for any comparison (SMD < 0.03). By contrast, RT induced greater type I and type II muscle fiber hypertrophy than CT when high-intensity interval training (HIIT) was incorporated alone (SMD > 0.33) or combined with continuous ET (SMD > 0.27), but not compared with CT incorporating only continuous ET (SMD < 0.16). The subgroup analyses of this systematic review and meta-analysis showed that RT induces greater muscle fiber hypertrophy than CT when HIIT is included. However, no CT affected whole-muscle hypertrophy compared with RT.

Effects of Concurrent, Within-Session, Aerobic and Resistance Exercise Training on Functional Capacity and Muscle Performance in Elderly Male Patients with Chronic Heart Failure

BACKGROUND

The best format of exercise training (ET) in the setting of cardiac rehabilitation in patients with chronic heart failure (CHF) is still to be defined. Current guidelines recommend aerobic exercises, such as running and cycling, including some sessions per week of resistance exercise.

AIM

The aim of this study was to address the effectiveness of a concurrent exercise training program utilizing a circuit of sequential endurance and resistance exercises on functional capacity and muscular strength in patients with CHF.

METHODS

Ninety-five consecutive male patients (age 63.1 ± 6 years) with CHF (EF < 40%) in NYHA functional class II/III, were randomly assigned on 1:1 basis to a 12-week aerobic continuous training (AT) or concurrent CT), aerobic + resistance, training (CT), three times a week, with each session lasting 80 min. We used high quality, specifically designed ergometers, connected with each other and governed by a central console, and managed by a single physiotherapist. Before and after training all patients performed a symptoms-limited exercise test on a treadmill and a 6-min walking test (6MWT). Patients in the CT group also performed resistance exercises of upper and lower body.

RESULTS

The 6MWT and exercise duration at ergometric test increased significantly in both AT and CT groups, with the increase being greater in CT group (p < 0.001; ES = 0.13; p < 0.01; ES = 0.07). Muscular strength increased significantly in the CT group, particularly in the lower body muscular districts (p < 0.001). Quality of life improved in both groups, with a significantly greater improvement in the CT group (p < 0.05). No side effects leading to discontinuation of training were observed.

CONCLUSIONS

These findings indicate that concurrent, within-session training results in larger improvements in functional capacity, in addition to muscle performance, in patients with CHF, in comparison to single-mode aerobic training.

Additional health education and nutrition management cause more weight loss than concurrent training in overweight young females

OBJECTIVE

This study aimed to compare the effect of concurrent training and the addition of health education and nutrition management on body composition and health-related outcomes.

METHODS

Twenty-four healthy overweight females (20.42 ± 1.02 years, body mass index [BMI] 25.83 ± 3.63 kg∙m^-2) were assigned to a concurrent training group (Exe, n = 12) or a concurrent training and health education group (Exe + Edu, n = 12). Both groups completed 8 weeks of concurrent training (6 days/week), whereas the Exe + Edu participants received additional health education and controlled daily energy intake within the basal metabolic rate. Body composition, serum glucose, lipids and related hormones were measured before and after intervention.

RESULTS

After intervention, the Exe group lost 2.47 kg (±2.46) of body mass, 2.44 kg (±1.71) of total fat mass (FM), corresponding to a body fat percentage (BF%) of 2.25%. Losses of body mass, total FM and BF% in the Exe + Edu group were -5.19 ± 1.87 kg, -4.42 ± 1.83 kg and -4.33 ± 2.39%, respectively. The Exe + Edu participants had significantly greater reductions of body mass, total FM, and trunk and leg FM relative to the Exe participants (p < 0.05). Serum glucose, lipids, insulin and progesterone levels were improved in both groups without group difference.

CONCLUSION

Concurrent training is an effective short-term training strategy for reducing FM and improving fasting glucose, blood lipids and related hormones. Furthermore, the combination of additional health education can achieve greater effects on weight loss and the reduction of total and regional FM, which may be a better obesity treatment method.

Acute effects of concurrent muscle power and sport-specific endurance exercises on markers of immunological stress response and measures of muscular fitness in highly trained youth male athletes

PURPOSE

To examine the acute effects of concurrent muscle power and sport-specific endurance exercises order on immunological stress responses, muscular-fitness, and rating-of-perceived-exertion (RPE) in highly trained youth male judo athletes.

METHODS

Twenty male participants randomly performed two concurrent training (CT) sessions; power-endurance and endurance-power. Measures of immune response (e.g., white blood cells), muscular-fitness (i.e., counter-movement-jump [CMJ]), RPE, blood-lactate, and -glucose were taken at different time-point (i.e., pre, mid, post, and post6h).

RESULTS

There were significant time*order interactions for white blood cells, lymphocytes, granulocytes, granulocyte-lymphocyte-ratio, and systemic-inflammation-index. Power-endurance resulted in significantly larger pre-to-post increases in white blood cells and lymphocytes while endurance-power resulted in significantly larger pre-to-post increases in the granulocyte-lymphocyte-ratio and systemic-inflammation-index. Likewise, significantly larger pre-to-post6h white blood cells and granulocytes increases were observed following power-endurance compared to endurance-power. Moreover, there was a significant time*order interaction for blood-glucose and -lactate. Following endurance-power, blood-lactate and -glucose increased from pre-to-mid but not from pre-to-post. Meanwhile, in power-endurance blood-lactate and -glucose increased from pre-to-post but not from pre-to-mid. A significant time*order interaction was observed for CMJ-force with larger pre-to-post decreases in endurance-power compared to power-endurance. Further, CMJ-power showed larger pre-to-mid performance decreases following power-endurance, compared to endurance-power. Regarding RPE, significant time*order interactions were noted with larger pre-to-mid values following endurance-power and larger pre-to-post values following power-endurance.

CONCLUSION

CT induced acute and delayed order-dependent immune cell count alterations in highly trained youth male judo athletes. In general, power-endurance induced higher acute and delayed immunological stress responses compared to endurance-power. CMJ-force and RPE fluctuated during both CT sessions but went back to baseline 6 h post-exercise.

Selective Effect of Different High-Intensity Running Protocols on Resistance Training Performance

ABSTRACT

Pérez-Castilla, A, García-Pinillos, F, Miras-Moreno, S, Ramirez-Campillo, R, García-Ramos, A, and Ruiz-Alias, SA. Selective effect of different high-intensity running protocols on resistance training performance. J Strength Cond Res XX(X): 000-000, 2022-This study aimed to explore the acute effect of 2 high-intensity running protocols (high-intensity interval training [HIIT] and sprint interval training [SIT]) on resistance training (RT) performance and their combined effect on the lower-body maximal neuromuscular capacities. Eighteen healthy subjects randomly completed 3 experimental protocols: only RT, HIIT + RT, and SIT + RT. Characteristics of the RT protocol include 3 back-squat sets of 10 repetitions or 20% velocity loss against 60% of 1 repetition maximum with 3 minutes of interset rest. Characteristics of the high-intensity running protocols include HIIT (4 intervals of 4 minutes at ∼110% of functional threshold power with 3 minutes of interinterval rest) and SIT (6 all-out sprints of 30 seconds with 4 minutes and 24 seconds of interinterval rest). The force-velocity relationship (maximal values of force [F0], velocity [v0], and power [Pmax]) was evaluated at the beginning and at the end of each experimental protocol. The number of back-squat repetitions (p = 0.006; effect size [ES] = -0.96), fastest velocity (p = 0.003; ES = -0.63), and average velocity (p = 0.001; ES = -0.73) were lower for the SIT + RT protocol compared with the RT protocol, but no significant differences were observed between the RT and HIIT + RT (p ≥T0.057; ES ≤.-0.46, except -0.82 for the number of back-squat repetitions) and HIIT + RT and SIT + RT (p ≥T0.091; ES .0-0.35) protocols. The 3 protocols induced comparable decreases in v0 and Pmax (F(2,34) 2,0.96; p ≥ 0.393), but F0 tended to decrease after the SIT + RT protocol and to increase after the RT and HIIT + RT protocols (F(2,34) = 4.37; p = 0.035). Compared with RT alone, the data suggest that SIT deteriorates RT quality and F0 capacity more than long-interval HIIT.

Effects of Concurrent Strength and HIIT-Based Endurance Training on Physical Fitness in Trained Team Sports Players: A Systematic Review and Meta-Analysis

BACKGROUND

Concurrent strength and HIIT-based endurance training (CT) has merit in time-saving in team sports. However, the effect of CT on physical fitness remained equivocal. This meta-analysis aimed to determine whether CT would produce an interference effect on the development of physical fitness when compared to strength training (ST) or HIIT-based endurance training (HET) alone in trained team sports players.

METHODS

A total of 2478 studies from three databases were screened. 52 full texts were reviewed. Seven studies were finally included and then subgroups were used for quantitative analysis.

RESULTS

Compared to ST alone, CT had a significant effect on the development of maximal lower-body strength in trained team sports players (MD 4.20 kg, 95% CI 0.71-7.68, p = 0.02, I² = 20%), but there was no significant difference between the groups on training adaptation in lower-body power (SMD 0.08, 95% CI -0.23-0.39, p = 0.62, I² = 26%). Furthermore, a sub-group analysis based on the internal organization order of CT revealed that there was no statistically significant subgroup effect between CT and ST alone in all parameters.

CONCLUSIONS

Well-designed CT regimens did not interfere with the development of physical fitness of trained team sports players.

Effects of Running-Specific Strength Training, Endurance Training, and Concurrent Training on Recreational Endurance Athletes' Performance and Selected Anthropometric Parameters

OBJECTIVE

The present study aimed to verify the effects of running-specific strength training alone, endurance training alone, and concurrent training on recreational endurance athletes' performance and selected anthropometric parameters.

METHOD

Thirty male recreational endurance runners were randomly assigned using a blocking technique to either a running-specific strength training group (RSSTG), an endurance training group (ETG), or a concurrent training group (CTG). RSSTG performed three strength-training sessions per week orientated to running, ETG underwent three endurance sessions per week, and CTG underwent a 3-day-per-week concurrent training program performed on non-consecutive days, alternating the strength and endurance training sessions applied to RSSTG and ETG. The training protocol lasted 12 weeks and was designed using the ATR (Accumulation, Transmutation, Realization) block periodization system. The following assessments were conducted before and after the training protocol: body mass (BM), body mass index (BMI), body fat percentage (BFP), lean mass (LM), countermovement jump (CMJ), 1RM (one-repetition maximum) squat, running economy at 12 and 14 km/h (RE12 and RE14), maximum oxygen consumption (VO₂max), and anaerobic threshold (AnT).

RESULTS

RSSTG significantly improved the results in CMJ, 1RM squat, RE12, and RE14. ETG significantly improved in RE12, RE14, VO₂max, and AnT. Finally, CTG, obtained significant improvements in BFP, LM, CMJ, 1RM squat, RE12, RE14, VO₂max, and AnT. RSSTG obtained improvements significantly higher than ETG in CMJ, 1RM squat, and RE14. ETG results were significantly better than those attained by RSSTG in AnT. Moreover, CTG marks were significantly higher than those obtained by ETG in CMJ and RE14.

CONCLUSION

Performing a 12-week concurrent training program integrated into the ATR periodization system effectively improves body composition and performance variables that can be obtained with exclusive running-specific strength and endurance training in recreational runners aged 30 to 40. Running-specific strength training enhances maximum and explosive strength and RE, whereas exclusive endurance training improves VO₂max, AnT, and RE. Performing concurrent training on non-consecutive days effectively prevents the strength and endurance adaptations attained with single-mode exercise from being attenuated. The ATR periodization system is useful in improving recreational endurance athletes' performance parameters, especially when performing concurrent training programs.

Effects of Cycling Intensity on Acute Signaling Adaptations to 8-weeks Concurrent Training in Trained Cyclists

This study examined whether the intensity of endurance stimuli modifies the adaptation in strength and endurance following concurrent training and whether the acute molecular response to concurrent exercise is affected by training status. Using a parallel group design, trained cyclists were randomized to either resistance exercise followed by moderate intensity continuous training (RES + MICT, n = 6), or resistance exercise followed by work matched high intensity interval training (RES + HIIT, n = 7), across an 8 weeks training programme. A single RES + MICT or RES + HIIT exercise stimulus was completed 1 week before and within 5 days of completing the training programme, to assess phosphorylation of protein kinases of the mTOR and AMPK signaling pathways. There were no main effects of time or group on the phosphorylation of protein kinases in response to concurrent exercise stimulus pre- and post-training intervention (p > 0.05). Main effects of time were observed for all maximal strength exercises; back-squat, split-squat, and calf-raise (p < 0.001), with all improving post intervention. A time × group interaction was present for V̇O_2peak, with the RES + MICT group displaying a preferential response to that of the RES + HIIT group (p = 0.010). No time nor group effects were observed for 5 min time trial performance, power at 2 and 4 mmol L⁻¹ (p > 0.05). Whilst preliminary data due to limited sample size the intensity of endurance activity had no effect on performance outcomes, following concurrent training. Further, the acute molecular response to a concurrent exercise stimulus was comparable before and after the training intervention, suggesting that training status had no effect on the molecular responses assessed.

Acute Effects of Aerobic Exercise on Muscle Strength and Power in Trained Male Individuals: A Systematic Review with Meta-analysis

BACKGROUND

Concurrent training can be an effective and time-efficient method to improve both muscle strength and aerobic capacity. A major challenge with concurrent training is how to adequately combine and sequence strength exercise and aerobic exercise to avoid interference effects. This is particularly relevant for athletes.

OBJECTIVE

We aimed to examine the acute effects of aerobic exercise on subsequent measures of muscle strength and power in trained male individuals.

DESIGN

We performed a systematic review with meta-analysis.

DATA SOURCES

Systematic literature searches in the electronic databases PubMed, Web of Science, and Google Scholar were conducted up to July 2021.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies were included that applied a within-group repeated-measures design and examined the acute effects of aerobic exercise (i.e., running, cycling exercise) on subsequent measures of lower limb muscle strength (e.g., maximal isometric force of the knee extensors) and/or proxies of lower limb muscle power (e.g., countermovement jump height) in trained individuals.

RESULTS

Fifteen studies met the inclusion criteria. Aerobic exercise resulted in moderate declines in muscle strength (standardized mean difference [SMD] = 0.79; p = 0.003). Low-intensity aerobic exercise did not moderate effects on muscle strength (SMD = 0.65; p = 0.157) while moderate-to-high intensity aerobic exercise resulted in moderate declines in muscle strength (SMD = 0.65; p = 0.020). However, the difference between subgroups was not statistically significant (p = 0.979). Regarding aerobic exercise duration, large declines in muscle strength were found after > 30 min (SMD = 1.02; p = 0.049) while ≤ 30 min of aerobic exercise induced moderate declines in muscle strength (SMD = 0.59; p = 0.013). The subgroup difference was not statistically significant (p = 0.204). Cycling exercise resulted in significantly larger decrements in muscle strength (SMD = 0.79; p = 0.002) compared with running (SMD = 0.28; p = 0.035). The difference between subgroups was statistically significant (p < 0.0001). For muscle power, aerobic exercise did not result in any statistically significant changes (SMD = 0.04; p = 0.846).

CONCLUSIONS

Aerobic exercise induced moderate declines in measures of muscle strength with no statistically significant effects on proxies of muscle power in trained male individuals. It appears that higher compared with lower intensity as well as longer compared with shorter aerobic exercise duration exacerbate acute declines in muscle strength. Our results provide evidence for acute interference effects when aerobic exercies is performed before strength exercises. These findings may help practitioners to better prescribe single training sessions, particularly if environmental and/or infrastructural reasons (e.g., availability of training facilities) do not allow the application of strength training before aerobic exercise.

Minimal-Dose Resistance Training for Improving Muscle Mass, Strength, and Function: A Narrative Review of Current Evidence and Practical Considerations

Resistance training (RT) is the only non-pharmacological intervention known to consistently improve, and therefore offset age-related declines in, skeletal muscle mass, strength, and power. RT is also associated with various health benefits that are underappreciated compared with the perceived benefits of aerobic-based exercise. For example, RT participation is associated with reduced all-cause and cancer-related mortality and reduced incidence of cardiovascular disease, hypertension, and symptoms of both anxiety and depression. Despite these benefits, participation in RT remains low, likely due to numerous factors including time constraints, a high-perceived difficulty, and limited access to facilities and equipment. Identification of RT strategies that limit barriers to participation may increase engagement in RT and subsequently improve population health outcomes. Across the lifespan, declines in strength and power occur up to eight times faster than the loss of muscle mass, and are more strongly associated with functional impairments and risks of morbidity and mortality. Strategies to maximise healthspan should therefore arguably focus more on improving or maintaining muscle strength and power than on increasing muscle mass per se. Accumulating evidence suggests that minimal doses of RT, characterised by lower session volumes than in traditional RT guidelines, together with either (1) higher training intensities/loads performed at lower frequencies (i.e. low-volume, high-load RT) or (2) lower training intensities/loads performed at higher frequencies and with minimal-to-no equipment (i.e. resistance 'exercise snacking'), can improve strength and functional ability in younger and older adults. Such minimal-dose approaches to RT have the potential to minimise various barriers to participation, and may have positive implications for the feasibility and scalability of RT. In addition, brief but frequent minimal-dose RT approaches (i.e. resistance 'exercise snacking') may provide additional benefits for interrupting sedentary behaviour patterns associated with increased cardiometabolic risk. Compared to traditional approaches, minimal-dose RT may also limit negative affective responses, such as increased discomfort and lowered enjoyment, both of which are associated with higher training volumes and may negatively influence exercise adherence. A number of practical factors, including the selection of exercises that target major muscle groups and challenge both balance and the stabilising musculature, may influence the effectiveness of minimal-dose RT on outcomes such as improved independence and quality-of-life in older adults. This narrative review aims to summarise the evidence for minimal-dose RT as a strategy for preserving muscle strength and functional ability across the lifespan, and to discuss practical models and considerations for the application of minimal-dose RT approaches.

Effects of High-Intensity Interval Training With Specific Techniques on Jumping Ability and Change of Direction Speed in Karate Athletes: An Inter-individual Analysis

This study investigated the effect of 4weeks of high-intensity interval training (HIIT) with specific techniques and analyzed inter-individual variability [classified in responders (Rs) and non-responders (NRs)] on jumping ability and change of direction speed (CODS) in youth karate athletes. Athletes of both genders (n=10) were randomly assigned into experimental group (EG; n=5) and the control group (CG; n=5). The EG trained 2-3days per week applying HIIT (three rounds [15 sets of 4s all-out specific efforts with 8s of dynamical pauses] with 3min of recovery between rounds) during their usual training during 4weeks. Assessments included squat jump (SJ) and countermovement jump (CMJ) and CODS by T-test. No significant interaction effect group by time was found. Although, in percentage and effect size (ES) terms increases were reported in both groups for SJ (EG: 15.2%, ES=0.91 vs. CG: 12.4%, ES=0.02) and only in EG for the T-test (-1.7%; ES=-0.35). In turn, a trend toward a higher proportion of Rs was observed in the EG (40% Rs) vs. CG (20% Rs) for SJ and CODS, respectively. In conclusion, the addition to regular training of a HIIT with specific techniques and based on the temporal combat structure after 4weeks was not a sufficient stimulus to increase jumping ability and CODS in karate athletes.

The Effects of Sprint vs. Resisted Sled-Based Training; an 8-Week in-Season Randomized Control Intervention in Elite Rugby League Players

The aim of the current study was to examine the efficacy of resisted sled-based training compared to traditional unresisted sprint training in terms of mediating improvements in speed, agility, and power during an eight-week period of in-season training in elite rugby league players. Participants were randomly separated into either resisted sled or traditional sprint-based training groups and they completed an eight-week in-season training block with training prescribed based on the group to which they were assigned. Measures of 5 m, 10 m, and 20 m sprint times in addition to countermovement jump height and 505-agility test time were measured at baseline, four-weeks and eight-weeks. For sprint-based outcomes, although both groups improved significantly, there were no statistical differences between the two training methods. However, at the eight-week time point there were significant improvements in 505-agility test (sprint group: baseline = 2.45 and eight-weeks = 2.42 s/sled group: baseline = 2.43 and eight-weeks = 2.37 s) and countermovement jump (sprint group: baseline = 39.18 and eight-weeks = 39.49 cm/sled group: baseline = 40.43 and eight-weeks = 43.07 cm) performance in the sled training group. Therefore, the findings from this investigation may be important to strength and conditioning coaches working in an elite rugby league in that resisted sled training may represent a more effective method of sprint training prescription.

Myofibre Hypertrophy in the Absence of Changes to Satellite Cell Content Following Concurrent Exercise Training in Young Healthy Men

Concurrent exercise training has been suggested to create an ‘interference effect,’ attenuating resistance training-based skeletal muscle adaptations, including myofibre hypertrophy. Satellite cells support myofibre hypertrophy and are influenced by exercise mode. To determine whether satellite cells contribute to the ‘interference effect’ changes in satellite cell and myonuclear content were assessed following a period of training in 32 recreationally active males (age: 25 ± 5 year; body mass index: 24 ± 3 kg⋅m^–2; mean ± SD) who undertook 12-week of either isolated (3 d⋅w^–1) resistance (RES; n = 10), endurance (END; n = 10), or alternate day (6 d⋅w^–1) concurrent (CET, n = 12) training. Skeletal muscle biopsies were obtained pre-intervention and after 2, 8, and 12 weeks of training to determine fibre type-specific cross-sectional area (CSA), satellite cell content (Pax7⁺DAPI⁺), and myonuclei (DAPI⁺) using immunofluorescence microscopy. After 12 weeks, myofibre CSA increased in all training conditions in type II (P = 0.0149) and mixed fibres (P = 0.0102), with no difference between conditions. Satellite cell content remained unchanged after training in both type I and type II fibres. Significant correlations were observed between increases in fibre type-specific myonuclear content and CSA of Type I (r = 0.63, P < 0.0001), Type II (r = 0.69, P < 0.0001), and mixed fibres (r = 0.72, P < 0.0001). Resistance, endurance, and concurrent training induce similar myofibre hypertrophy in the absence of satellite cell and myonuclear pool expansion. These findings suggest that myonuclear accretion via satellite cell fusion is positively correlated with hypertrophy after 12 weeks of concurrent training, and that individuals with more myonuclear content displayed greater myofibre hypertrophy.

Modelling performance with exponential functions in elite short-track speed skaters

Mathematical models are used to describe and predict the effects of training on performance. The initial models are structured by impulse-type transfer functions, however, cellular adaptations induced by exercise may exhibit exponential kinetics for their growth and subsequent dissipation. Accumulation of exercise bouts counteracts dissipation and progressively induces structural and functional changes leading to performance improvement. This study examined the suitability of a model with exponential terms (Exp-Model) in elite short-track speed (ST) skaters. Training loads and performance evolution from fifteen athletes (10 males, 5 females) were previously collected over a 3-month training period. Here, we computed the relationship between training loads and performance with Exp-Model and compared with previous results obtained with a variable dose-response model (Imp-Model). Exp-Model showed a higher correlation between actual and modelled performances (R² = 0.83 ± 0.08 and 0.76 ± 0.07 for Exp-Model and Imp-Model, respectively). Concerning model parameters, a higher τA1 (time constant for growth) value was found (p = 0.0047; d = 1.4; 95% CI [0.4;1.9]) in males compared to females with Exp-model, suggesting that females have a faster adaptative response to training loads. Thus, according to this study, Exp-model may better describe training adaptations in elite ST athletes than Imp-Model.

Development of Maximal Dynamic Strength During Concurrent Resistance and Endurance Training in Untrained, Moderately Trained, and Trained Individuals: A Systematic Review and Meta-analysis

Background

The effect of concurrent training on the development of maximal strength is unclear, especially in individuals with different training statuses.

Objective

The aim of this systematic review and meta-analysis study was to compare the effect of concurrent resistance and endurance training with that of resistance training only on the development of maximal dynamic strength in untrained, moderately trained, and trained individuals.

Methods

On the basis of the predetermined criteria, 27 studies that compared effects between concurrent and resistance training only on lower-body 1-repetition maximum (1RM) strength were included. The effect size (ES), calculated as the standardised difference in mean, was extracted from each study, pooled, and analysed with a random-effects model.

Results

The 1RM for leg press and squat exercises was negatively affected by concurrent training in trained individuals (ES =  – 0.35, p < 0.01), but not in moderately trained ( – 0.20, p = 0.08) or untrained individuals (ES = 0.03, p = 0.87) as compared to resistance training only. A subgroup analysis revealed that the negative effect observed in trained individuals occurred only when resistance and endurance training were conducted within the same training session (ES same session =  – 0.66, p < 0.01 vs. ES different sessions =  – 0.10, p = 0.55).

Conclusion

This study demonstrated the novel and quantifiable effects of training status on lower-body strength development and shows that the addition of endurance training to a resistance training programme may have a negative impact on lower-body strength development in trained, but not in moderately trained or untrained individuals. This impairment seems to be more pronounced when training is performed within the same session than in different sessions. Trained individuals should therefore consider separating endurance from resistance training during periods where the development of dynamic maximal strength is prioritised.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40279-021-01426-9.

Molecular Regulation of Skeletal Muscle Growth and Organelle Biosynthesis: Practical Recommendations for Exercise Training

The regulation of skeletal muscle mass and organelle homeostasis is dependent on the capacity of cells to produce proteins and to recycle cytosolic portions. In this investigation, the mechanisms involved in skeletal muscle mass regulation-especially those associated with proteosynthesis and with the production of new organelles-are presented. Thus, the critical roles of mammalian/mechanistic target of rapamycin complex 1 (mTORC1) pathway and its regulators are reviewed. In addition, the importance of ribosome biogenesis, satellite cells involvement, myonuclear accretion, and some major epigenetic modifications related to protein synthesis are discussed. Furthermore, several studies conducted on the topic of exercise training have recognized the central role of both endurance and resistance exercise to reorganize sarcomeric proteins and to improve the capacity of cells to build efficient organelles. The molecular mechanisms underlying these adaptations to exercise training are presented throughout this review and practical recommendations for exercise prescription are provided. A better understanding of the aforementioned cellular pathways is essential for both healthy and sick people to avoid inefficient prescriptions and to improve muscle function with emergent strategies (e.g., hypoxic training). Finally, current limitations in the literature and further perspectives, notably on epigenetic mechanisms, are provided to encourage additional investigations on this topic.

Weight Loss after 12 Weeks of Exercise and/or Nutritional Guidance Is Not Obligatory for Induced Changes in Local Fat/Lean Mass Indexes in Adults with Excess of Adiposity

The objectives of this secondary analysis are (1) to investigate the differential effects of exercise training modalities-high-intensity interval training (HIIT), resistance training (RT), combined training (CT = HIIT + RT), and/or nutritional guidance (NG) alone-on local fat/lean mass indexes in adults with excess of adiposity; (2) to identify the individual patterns of response based on either a clinical criterion of weight loss (≥5%) and/or technical error (TE) of measurement of local fat/lean mass indexes; and (3) to assess the individual change for body composition parameters assigned either to HIIT, RT, CT, and/or NG groups utilizing a TE. A 12-week trial was conducted in 55 participants randomized to one of the four interventions. The primary outcome was clinical change in body weight (i.e., weight loss of ≥5%). Secondary outcomes included change in ratio of android and gynoid fat mass, as well as local fat and lean mass indexes (arms, trunk, and legs), before and after intervention. The main findings from the current analysis revealed that (i) after 12 weeks of follow-up, significant decreases in several body composition indexes were found including body weight, arm, trunk, and legs fat mass, and android and gynecoid fat mass were observed in HIIT, RT, and CT groups (p < 0.05); (ii) a significant proportion of individuals showed a positive response following 12 weeks of training, led by the HIIT group with 44% and followed by RT with 39% in 9 indexes; (iii) the HIIT group showed lowest rates of adverse responders with (6%); and (iv) the individual patterns of response utilizing clinically meaningful weight loss were not necessarily associated with the corresponding individual training-induced changes in body composition indexes in adults with excess of adiposity. Overall, the study suggests that HIIT has an important ability to reduce the prevalence of non-response to improve body composition indexes.

Order of same-day concurrent training influences some indices of power development, but not strength, lean mass, or aerobic fitness in healthy, moderately-active men after 9 weeks of training

Background

The importance of concurrent exercise order for improving endurance and resistance adaptations remains unclear, particularly when sessions are performed a few hours apart. We investigated the effects of concurrent training (in alternate orders, separated by ~3 hours) on endurance and resistance training adaptations, compared to resistance-only training.

Materials and methods

Twenty-nine healthy, moderately-active men (mean ± SD; age 24.5 ± 4.7 y; body mass 74.9 ± 10.8 kg; height 179.7 ± 6.5 cm) performed either resistance-only training (RT, n = 9), or same-day concurrent training whereby high-intensity interval training was performed either 3 hours before (HIIT+RT, n = 10) or after resistance training (RT+HIIT, n = 10), for 3 d^.wk^-1 over 9 weeks. Training-induced changes in leg press 1-repetition maximal (1-RM) strength, countermovement jump (CMJ) performance, body composition, peak oxygen uptake (V˙O2peak), aerobic power (W˙peak), and lactate threshold (W˙LT) were assessed before, and after both 5 and 9 weeks of training.

Results

After 9 weeks, all training groups increased leg press 1-RM (~24–28%) and total lean mass (~3-4%), with no clear differences between groups. Both concurrent groups elicited similar small-to-moderate improvements in all markers of aerobic fitness (V˙O2peak ~8–9%; W˙LT ~16-20%; W˙peak ~14-15%). RT improved CMJ displacement (mean ± SD, 5.3 ± 6.3%), velocity (2.2 ± 2.7%), force (absolute: 10.1 ± 10.1%), and power (absolute: 9.8 ± 7.6%; relative: 6.0 ± 6.6%). HIIT+RT elicited comparable improvements in CMJ velocity only (2.2 ± 2.7%). Compared to RT, RT+HIIT attenuated CMJ displacement (mean difference ± 90%CI, -5.1 ± 4.3%), force (absolute: -8.2 ± 7.1%) and power (absolute: -6.0 ± 4.7%). Only RT+HIIT reduced absolute fat mass (mean ± SD, -11.0 ± 11.7%).

Conclusions

In moderately-active males, concurrent training, regardless of the exercise order, presents a viable strategy to improve lower-body maximal strength and total lean mass comparably to resistance-only training, whilst also improving indices of aerobic fitness. However, improvements in CMJ displacement, force, and power were attenuated when RT was performed before HIIT, and as such, exercise order may be an important consideration when designing training programs in which the goal is to improve lower-body power.

Concurrent Training for Sports Performance: The 2 Sides of the Medal

The classical work by Robert C. Hickson showed in 1980 that the addition of a resistance-training protocol to a predominantly aerobic program could lead to impaired leg-strength adaptations in comparison with a resistance-only training regimen. This interference phenomenon was later highlighted in many reports, including a meta-analysis. However, it seems that the interference effect has not been consistently reported, probably because of the complex interactions between training variables and methodological issues. On the other side of the medal, Dr Hickson et al subsequently (1986) reported that a strength-training mesocycle could be beneficial for endurance performance in running and cycling. In recent meta-analyses and review articles, it was demonstrated that such a training strategy could improve middle- and long-distance performance in many disciplines (running, cycling, cross-country skiing, and swimming). Notably, it appears that improvements in the energy cost of locomotion could be associated with these performance enhancements. Despite these benefits, it was also reported that strength training could represent a detrimental stimulus for endurance performance if an inappropriate training plan has been prepared. Taken together, these observations suggest that coaches and athletes should be careful when concurrent training seems imperative to meet the complex physiological requirements of their sport. This brief review presents a practical appraisal of concurrent training for sports performance. In addition, recommendations are provided so that practitioners can adapt their interventions based on the training objectives.

A Brief Review on Concurrent Training: From Laboratory to the Field

The majority of sports rely on concurrent training (CT; e.g., the simultaneous training of strength and endurance). However, a phenomenon called “Concurrent training effect” (CTE), which is a compromise in adaptation resulting from concurrent training, appears to be mostly affected by the interference of the molecular pathways of the underlying adaptations from each type of training segments. Until now, it seems that the volume, intensity, type, frequency of endurance training, as well as the training history and background strongly affect the CTE. High volume, moderate, continuous and frequent endurance training, are thought to negatively affect the resistance training-induced adaptations, probably by inhibition of the Protein kinase B—mammalian target of rapamycin pathway activation, of the adenosine monophosphate-activated protein kinase (AMPK). In contrast, it seems that short bouts of high-intensity interval training (HIIT) or sprint interval training (SIT) minimize the negative effects of concurrent training. This is particularly the case when HIIT and SIT incorporated in cycling have even lower or even no negative effects, while they provide at least the same metabolic adaptations, probably through the peroxisome proliferator-activated receptor-γ coactivator (PGC-1a) pathway. However, significant questions about the molecular events underlying the CTE remain unanswered.

The Effects of Concurrent Strength and Endurance Training on Physical Fitness and Athletic Performance in Youth: A Systematic Review and Meta-Analysis

Combining training of muscle strength and cardiorespiratory fitness within a training cycle could increase athletic performance more than single-mode training. However, the physiological effects produced by each training modality could also interfere with each other, improving athletic performance less than single-mode training. Because anthropometric, physiological, and biomechanical differences between young and adult athletes can affect the responses to exercise training, young athletes might respond differently to concurrent training (CT) compared with adults. Thus, the aim of the present systematic review with meta-analysis was to determine the effects of concurrent strength and endurance training on selected physical fitness components and athletic performance in youth. A systematic literature search of PubMed and Web of Science identified 886 records. The studies included in the analyses examined children (girls age 6–11 years, boys age 6–13 years) or adolescents (girls age 12–18 years, boys age 14–18 years), compared CT with single-mode endurance (ET) or strength training (ST), and reported at least one strength/power—(e.g., jump height), endurance—(e.g., peak V°O₂, exercise economy), or performance-related (e.g., time trial) outcome. We calculated weighted standardized mean differences (SMDs). CT compared to ET produced small effects in favor of CT on athletic performance (n = 11 studies, SMD = 0.41, p = 0.04) and trivial effects on cardiorespiratory endurance (n = 4 studies, SMD = 0.04, p = 0.86) and exercise economy (n = 5 studies, SMD = 0.16, p = 0.49) in young athletes. A sub-analysis of chronological age revealed a trend toward larger effects of CT vs. ET on athletic performance in adolescents (SMD = 0.52) compared with children (SMD = 0.17). CT compared with ST had small effects in favor of CT on muscle power (n = 4 studies, SMD = 0.23, p = 0.04). In conclusion, CT is more effective than single-mode ET or ST in improving selected measures of physical fitness and athletic performance in youth. Specifically, CT compared with ET improved athletic performance in children and particularly adolescents. Finally, CT was more effective than ST in improving muscle power in youth.

Physiological responses to partial-body cryotherapy performed during a concurrent strength and endurance session

This investigation examined the effect of partial-body cryostimulation (PBC) performed in the recovery time between a strength training and an interval running (IR) session. Nine rugby players (age, 23.7 ± 3.6 years; body mass index, 28.0 ± 2.6 kg·m^-2) were randomly exposed to 2 different conditions: (i) PBC: 3 min at -160 °C, and (ii) passive recovery at 21 °C. We performed the bioelectrical impedance analysis (BIA) and recorded temperature and cardiac autonomic variables at 3 time points: at baseline, after strength training, and after 90 min of recovery. In addition, blood lactate concentration was measured 1 min before and 2.5 min after the IR. Heart rate (HR), energy cost, minute ventilation, oxygen uptake, and metabolic power were assessed during the IR. Homeostatic hydration status was affected by the execution of an intense strength training subsession. Then, after PBC, the BIA vector was restored close to normohydration status. Autonomic variables changed over time in both conditions, although the mean differences and effect sizes were greater in the PBC condition. During IR, HR was 3.5% lower after PBC, and the same result was observed for oxygen uptake (∼4.9% lower) and ventilation (∼6.5% lower). The energy cost measured after cryotherapy was ∼9.0% lower than after passive recovery. Cryotherapy enhances recovery after a single strength training session, and during subsequent IR, it shows a reduction in cardiorespiratory and metabolic parameters. PBC may be useful for those athletes who compete or train more than once in the same day, to improve recovery between successive training sessions or competitions.

The compatibility of concurrent high intensity interval training and resistance training for muscular strength and hypertrophy: a systematic review and meta-analysis

The purpose of this systematic review and meta-analysis is to assess the effect of concurrent high intensity interval training (HIIT) and resistance training (RT) on strength and hypertrophy. Five electronic databases were searched using terms related to HIIT, RT, and concurrent training. Effect size (ES), calculated as standardised differences in the means, were used to examine the effect of concurrent HIIT and RT compared to RT alone on muscle strength and hypertrophy. Sub-analyses were performed to assess region-specific strength and hypertrophy, HIIT modality (cycling versus running), and inter-modal rest responses. Compared to RT alone, concurrent HIIT and RT led to similar changes in muscle hypertrophy and upper body strength. Concurrent HIIT and RT resulted in a lower increase in lower body strength compared to RT alone (ES = -0.248, p = 0.049). Sub analyses showed a trend for lower body strength to be negatively affected by cycling HIIT (ES = -0.377, p = 0.074) and not running (ES = -0.176, p = 0.261). Data suggests concurrent HIIT and RT does not negatively impact hypertrophy or upper body strength, and that any possible negative effect on lower body strength may be ameliorated by incorporating running based HIIT and longer inter-modal rest periods.