Current Guidelines for the Implementation of Flywheel Resistance Training Technology in Sports: A Consensus Statement.

BACKGROUND: Flywheel resistance training has become more integrated within resistance training programs in a variety of sports due to the neuromuscular, strength, and task-specific enhancements reported with this training. OBJECTIVE: This paper aimed to present the consensus reached by internationally recognized experts during a meeting on current definitions and guidelines for the implementation of flywheel resistance training technology in sports. METHODS: Nineteen experts from different countries took part in the consensus process; 16 of them were present at the consensus meeting (18 May 2023) while three submitted their recommendations by e-mail. Prior to the meeting, evidence summaries were developed relating to areas of priority. This paper discusses the available evidence and consensus process from which recommendations were made regarding the appropriate use of flywheel resistance training technology in sports. The process to gain consensus had five steps: (1) performing a systematic review of systematic reviews, (2) updating the most recent umbrella review published on this topic, (3) first round discussion among a sample of the research group included in this consensus statement, (4) selection of research group members-process of the consensus meeting and formulation of the recommendations, and (5) the consensus process. The systematic analysis of the literature was performed to select the most up-to-date review papers available on the topic, which resulted in nine articles; their methodological quality was assessed according to AMSTAR 2 (Assessing the Methodological Quality of Systematic Review 2) and GRADE (Grading Recommendations Assessment Development and Evaluation). Statements and recommendations scoring 7-9 were considered appropriate. RESULTS: The recommendations were based on the evidence summary and researchers' expertise; the consensus statement included three statements and seven recommendations for the use of flywheel resistance training technology. These statements and recommendations were anonymously voted on and qualitatively analyzed. The three statements reported a score ranging from 8.1 to 8.8, and therefore, all statements included in this consensus were considered appropriate. The recommendations (1-7) had a score ranging from 7.7 to 8.6, and therefore, all recommendations were considered appropriate. CONCLUSIONS: Because of the consensus achieved among the experts in this project, it is suggested that practitioners and researchers should adopt the guidelines reported in this consensus statement regarding the use of flywheel resistance technology in sports.

Eccentric overload differences between loads and training variables on flywheel training.

There is considerable debate about the existence of a real eccentric overload in flywheel exercises. This study aimed to analyse the differences in concentric: eccentric mechanical output ratios between different loads and variables in the flywheel squat exercise. Twenty physically active men (22.9 ± 2.2 years, height: 1.8 ± 0.1 m, weight: 79.6 ± 8.2 kg) performed a loading test using five moments of inertia. Angular speed was measured using a rotary encoder, while the vertical force was measured using force plates. For each variable (angular speed, angular acceleration, power, vertical force, and torque), mean and peak values were calculated for concentric and eccentric phases to allow comparisons across the loads. We tested the possible differences in Load × Phase (concentric and eccentric) and Load × Variable. The level of significance was established as p < 0.05. A significant Load × Phase interaction was found in mean angular speed, peak vertical force, peak angular acceleration, peak power and peak torque. Higher eccentric overload values were observed with speed-derived variables (angular speed, angular acceleration and power). In conclusion, speed-derived peak variables and lower loads are more likely to show an eccentric overload and can be used to monitor responses to flywheel training.

Effects of 6 weeks in-season flywheel squat resistance training on strength, vertical jump, change of direction and sprint performance in professional female soccer players.

Flywheel resistance training devices (FRTD) is shown effective in improving strength, sprinting, jumping and changes of direction (COD) performance in male soccer players, however, this is not elucidated in female soccer players. We aimed to assess the effect of FRTD on these physical abilities in females soccer players. 24 professional female soccer players (age: 20.4 ± 2.6 years) were randomly assigned to a flywheel training group (FWTG) that trained twice a week for 6 weeks on a rotary inertia device with an initial volume of 3 sets of 6 repetitions and an inertia of 0,025 kg · m-2, increasing intensity and volume or a control group (CG) that did not performed any additional resistance training program. Concentric peak torque of the knee extensors (CONEXT) and flexors (CONFLEX), eccentric peak torque of the knee extensors (ECCEXT) and flexors (ECCFLEX) at 60° · s-1 on an isokinetic dynamometer, countermovement jump (CMJ) height, COD and 30-metres sprint were assessed. Significant time by group interactions were found in CONEXT (p = 0.002; η²p = 0.425), CONFLEX (p = 0.037; η²p = 0.22), ECCEXT (p = 0.002; η²p = 0.43) and ECCFLEX (p = 0.008; η²p = 0.334). No time by group effect was found in CMJ (p = 0.061; η²p = 0.182), COD (p = 0.067; η²p = 0.184) or sprint (p = 0.926; η²p = 4.979 · e-4). In conclusion, 6 weeks of flywheel squat training improved strength (especially eccentric strength) but not soccer-specific abilities such as jumping, changing of direction or sprinting in professional soccer players.

Changes in Muscle Deoxygenation During Squat Exercise After 6-Week Resistance Training With Different Percentages of Velocity Loss.

ABSTRACT: Costilla, M, Casals, C, Marín-Galindo, A, Sánchez-Sixto, A, Muñoz-López, A, Sañudo, B, Corral-Pérez, J, and Ponce-González, JG. Changes in muscle deoxygenation during squat exercise after 6-week resistance training with different percentages of velocity loss. J Strength Cond Res 37(8): 1573-1580, 2023-The present study compared, for the first time, the effects of 6 weeks of 20% (20VL) vs. 40% (40VL) velocity loss (VL) resistance training (RT) programs on muscle oxygen dynamics during the squat exercise. Twenty-three young men (21.4 ± 2.4 years) were randomly allocated into the 20VL group ( n = 8), 40VL group ( n = 7), or control group (CG; n = 8). The RT program consisted of 3 sets of Smith machine back squat exercise at 20VL or 40VL with a 3-minute rest between sets, twice per week for 6 weeks. Tissue oxygenation index (TOI) was measured using near-infrared spectroscopy in the vastus medialis and vastus lateralis during a squat test (8-repetition 1 m·s -1 load test), and the maximum (maxTOI) and minimum (minTOI) TOIs were measured during a 3-min recovery period. After the 6-week RT program, TOI increased significantly at the beginning of the test in both muscles (during the first 4 repetitions in the vastus lateralis and 5 repetitions in the vastus medialis) in the 20VL group ( p < 0.05), with nonsignificant changes in the 40VL group and CG. The maxTOI was significantly increased in the vastus medialis (+3.76%) and vastus lateralis (+3.97%) after the training only in the 20VL group ( p < 0.05). The minTOI in the vastus medialis reached during the test remained unchanged postintervention for both training groups, with the CG showing significantly higher values compared with the 20VL group (+14.1%; p < 0.05). In conclusion, depending on the VL reached during a squat RT program, different changes in muscle oxygen dynamics can be expected. Training at 20% of VL improves metabolic efficiency and the reoxygenation peak after the set.

Stable vs. variable eccentric load. Do they induce different training and physical performance outcomes?

Since most movements on the field require athletes to produce forces in variable and unpredictable contexts, the use of training programs based on identical repetitions of an exercise may not be optimal for movement transference. Therefore, the aim of this study was to analyse the effects of unexpected eccentric load variability during resistance training in team sport players. Sixty-three men were randomly allocated to two experimental groups (Variable (VTG) and stable (STG) training group) and control group: (CG) volunteered to participate in this study. Experimental groups trained with the same average load of half-squat exercise twice a week for six weeks using rotary inertial devices (RIDs) with (VTG) and without (STG) an unexpected variability of the load. The squat force was measured for every session with force plates. Counter-movement jump (CMJ), sprint, and change of direction performances were measured pre and post-test. CMJ performance improved for VTG (p = .014; ES = 0.7) and STG (p = .005; ES = 0.79) but not for CG. Exposure to high eccentric forces with RIDs lead athletes to improve physical performance in the trained force vector but, since RIDs induce in high levels of variability per se, increasing the level of variability of the exercise will not add benefits to physical performance and training outcomes.HIGHLIGHTSThe relevance of the study is to analyse if increasing the variability of the load will improve the athlete output to different physical performance tests.The exposure to eccentric overload with RIDs during the squat exercise allows to greater CMJ height improvements than those seen in the literature with RIDs without overloading the eccentric contraction.RIDs induce in high level of variability per se. Therefore, increasing the level of variability of the exercise will not add benefits to physical performance and training outcomes.

The Flywheel Device Shaft Shape Determines Force and Velocity Profiles in The Half Squat Exercise.

Flywheel resistance training devices can be classified by their shaft shape. The objective of this study was to analyze whether using two flywheel resistance training devices shaft shapes can influence force and velocity production, regardless of the inertia used. Thirty-nine (n = 39) healthy active men participated in this study. They were randomized to perform 3 sets of 7 repetitions at maximal concentric voluntary execution, followed by a break in the last third of the eccentric phase in the half squat exercise. A progressive rotational inertial setting of 0.11, 0.22, and 0.33 kg·m2 was used. Force- and velocity-time profiles were captured using two force plates and a synchronized linear encoder. Statistical parametric mapping was used to compare biomechanical output between the flywheel devices. The level of significance was set at p < 0.05. Force application was significantly higher in the horizontal cylinder-shaped device for the three moments of inertia used in the eccentric phase (p < 0.001). In the concentric phase, force application was significantly higher in the horizontal cylinder-shaped device in 0.11 (p < 0.001) and 0.22 kg·m2 (p < 0.001). The resultant speed was higher in the vertical cone-shaped device in the concentric phase and the eccentric phase for the three moments of inertia (p < 0.001). In conclusion, the flywheel shaft type determines the mechanical output of the half squat exercise, regardless of the moment of inertia used. While a horizontal cylinder-shaped device is more suitable to achieve higher forces, especially in the eccentric phase, a vertical cone-shaped device can be used to achieve higher speeds during the execution of the exercise.

Effects of Different Velocity Loss Thresholds on Passive Contractile Properties and Muscle Oxygenation in the Squat Exercise Using Free Weights.

ABSTRACT: Muñoz-López, A, Marín-Galindo, A, Corral-Pérez, J, Costilla, M, Sánchez-Sixto, A, Sañudo, B, Casals, C, and Ponce-González, JG. Effects of different velocity loss thresholds on passive contractile properties and muscle oxygenation in the squat exercise using free weights. J Strength Cond Res 36(11): 3056-3064, 2022-The current study assessed the impact between different velocity loss thresholds on changes in the muscle contractile properties and muscle oxygenation after a single resistance training (RT) session. Thirty physically active men participated in a crossover study performing 3 sets of the squat exercise at a lifted speed of ≈0.75 m·s -1 , with 2 different velocity loss thresholds: 20% (VL20) vs 40% (VL40) in a randomized order. Contractile properties of the knee extensor muscles were tested using tensiomyography. In addition, muscle oxygenation was continuously measured from baseline until the end of the exercise session. The vastus lateralis showed a significant moment by condition interaction in time delay ( p = 0.044), muscle displacement ( p = 0.001), and contraction velocity ( p = 0.007), with greater reductions in VL40. In both trainings, oxygenated hemoglobin and tissue oxygen index decreased, whereas deoxygenated hemoglobin increased (moment as the main effect, p < 0.05), but without a moment by condition interaction. VL40 showed a lower deoxygenation slope in set 1 (-0.468%·s -1 , p = 0.001) and set 3 (-0.474%·s -1 , p = 0.037) as well as higher losses in set 1 (-41.50%, p = 0.003), set 2 (-41.84%, p = 0.002), and set 3 (-62.51%, p < 0.001), compared with VL20. No differences were found in the recovery period between conditions. In conclusion, during the RT program design, coaches and athletes should consider that VL40 produces higher mechanical and neuromuscular impairments than VL20, which seems to be necessary for hypertrophy to occur; however, VL40 also produces a longer period of lower oxygen supply than VL20, which can induce fast-to-slow muscle fiber transition.

Variability in the Application of Eccentric Force Using Different Rotary Inertia Devices May Influence the Treatment of Tendinopathy.

High intraset variability has been considered as a potential aid in the treatment of tendinopathy by producing forces in variable and unpredictable contexts that allow the athlete to return to sport pain free. The aim of this study was to compare the intraset variability in force profiles between different rotational inertia devices (RIDs) during concentric and eccentric (ECC) phases of movement and between different moments of inertia. Thirty-nine men performed a half-squat incremental test on 2 different RIDs: a horizontal cylinder and a vertical cone-shaped axis. Intraset variabilities in vertical force and velocity were analyzed using average coefficients of variation. RID squat exercise produced force intraset variability. The ECC phase of the movement showed more intraset variability in force output than the concentric phase. ECC vertical cone-shaped shaft showed a higher intraset variability in force than ECC horizontal cylinder-shaped shaft. This study demonstrated that using an RID to provide resistance in squat training of athletes produced a high intraset variability in the application of force.

The Maximum Flywheel Load: A Novel Index to Monitor Loading Intensity of Flywheel Devices.

BACKGROUND: The main aim of this study was (1) to find an index to monitor the loading intensity of flywheel resistance training, and (2) to study the differences in the relative intensity workload spectrum between the FW-load and ISO-load. METHODS: twenty-one males participated in the study. Subjects executed an incremental loading test in the squat exercise using a Smith machine (ISO-load) or a flywheel device (FW-load). We studied different association models between speed, power, acceleration, and force, and each moment of inertia was used to find an index for FW-load. In addition, we tested the differences between relative workloads among load conditions using a two-way repeated-measures test. RESULTS: the highest r2 was observed using a logarithmic fitting model between the mean angular acceleration and moment of inertia. The intersection with the x-axis resulted in an index (maximum flywheel load, MFL) that represents a theoretical individual maximal load that can be used. The ISO-load showed greater speed, acceleration, and power outcomes at any relative workload (%MFL vs. % maximum repetition). However, from 45% of the relative workload, FW-load showed higher vertical forces. CONCLUSIONS: MFL can be easily computed using a logarithmic model between the mean angular acceleration and moment of inertia to characterize the maximum theoretical loading intensity in the flywheel squat.

The use of real-time monitoring during flywheel resistance training programmes: how can we measure eccentric overload? A systematic review and meta-analysis.

This systematic review and meta-analysis aimed to analyse the technologies and main training variables used in the literature to monitor flywheel training devices in real time. In addition, as the main research question, we investigated how eccentric overload can be effectively monitored in relation to the training variable, flywheel shaft type device and the moment of inertia selected. The initial search resulted in 11,621 articles that were filtered to twenty-eight and seventeen articles that met the inclusion criteria for the systematic review and meta-analysis, respectively. The main technologies used included force sensors and rotary/linear encoders, mainly to monitor peak or mean force, power or speed. An eccentric overload was not always achieved using flywheel devices. The eccentric overload measurement was related to the main outcome selected. While mean force (p = 0.011, ES = -0.84) and mean power (p < 0.001, ES = -0.30) favoured the concentric phase, peak power (p < 0.001, ES = 0.78) and peak speed (p < 0.001, ES = 0.37) favoured the eccentric phase. In addition, the lower moments of inertia (i.e., from 0.01 to 0.2 kg·m2) and a cylindrical shaft type (i.e., vs conical pulley) showed higher possibilities to achieve eccentric overload. A wide variety of technologies can be used to monitor flywheel devices, but to achieve eccentric overload, a flywheel cylindrical shaft type with low moments of inertia is advised to be used.

Muscle Contractile Properties Measured at Submaximal Electrical Amplitudes and Not at Supramaximal Amplitudes Are Associated with Repeated Sprint Performance and Fatigue Markers.

BACKGROUND: The present study analyzes the associations between the muscle contractile properties (MCP) measured at different neuromuscular electrical stimulation amplitudes (NMESa) and the performance or transient fatigue after a bout of repeated sprints. METHODS: Seventeen physically active male subjects performed six repeated sprints of 30 m with 30 s of passive recovery. Capillary blood creatine kinase (CK) concentration, knee extension or flexion isometric peak torque, tensiomyography, and repeated sprint performance were assessed. RESULTS: Muscle displacement and contraction time were different in relation to the NMESa used in the rectus femoris and biceps femoris muscles. At rest, significant (p < 0.05) associations were found between muscle displacement and the loss of time in the repeated sprints (sprint performance) at 20 or 40 mA in the rectus femoris. At post +24 h or +48 h, the highest significant associations were found between the muscle displacement or the contraction time and CK or peak torques also at submaximal amplitudes (20 mA). The NMESa which elicits the peak muscle displacement showed lack of practical significance. CONCLUSION: Although MCP are typically assessed in tensiomyography using the NMESa that elicit peak muscle displacement, a submaximal NMESa may have a higher potential practical application to assess neuromuscular fatigue in response to repeated sprints.

Real-time mechanical responses to overload and fatigue using a flywheel training device.

PURPOSE: This study aimed to analyze mechanical performance and mechanical losses across different sets and repetitions of unilateral leg extensions under flywheel loading conditions. METHODS: In a cross-over design, 23 physically active participants executed 3 sets of 30 repetitions using two different loads. Angular speed, angular acceleration and power were monitored, and mean and peak values of these variables were calculated for each set of repetitions. We analyzed time-course differences every five repetitions (described as 'clusters'). Differences in the mechanical profile for Load by Set and in the mechanical losses for Load by Set by Cluster repetitions were analyzed using an ANOVA repeated measures test. A Principal Components (PC) analysis was also conducted. RESULTS: Only peak acceleration showed a significant Set by Load interaction (p = 0.006) in mechanical performance. At the intra-set level, all consecutive clusters showed a significant decrement in all variables, but with different magnitudes (speed < acceleration < power). Although all variables showed significant Set by Cluster and Load by Cluster interactions, only the acceleration variables showed a significant Set by Load interaction (p < 0.05). All the variables showed a single PC. Higher fatigue was found around the concentric peak for each variable. CONCLUSIONS: The most sensitive variable for detecting fatigue using real-time feedback seems to be the angular acceleration of the flywheel. Peak acceleration can be used to monitor training workload and training volume in real time in leg extension exercises using flywheel training devices.

Soccer Matches but Not Training Sessions Disturb Cardiac-Autonomic Regulation During National Soccer Team Training Camps.

Purpose: Heart rate variability (HRV) can be used to monitor changes in autonomic nervous system (ANS) function. Monitoring HRV via the natural log of the root-mean-square difference of successive normal RR intervals (lnRMSSD), a decrease was related to lower parasympathetic activity and a fatigued state, and an increase was related to higher parasympathetic activity and better physical conditioning. This study analyzed daily ANS function changes among professional soccer players at national team training camps during preparation for the UEFA Eurocup 2016. Method: 23 professional soccer players were distributed into two groups: First eleven (players who played more than 60 minutes per soccer match) and Reserves (the rest of the players). HRV and session training load (s-TL) were monitored. Between-group daily differences were assessed using two-way mixed repeated measures ANOVA. Results: s-TL significantly increased (p < .05) at the beginning of each camp and significantly decreased the day before the soccer match (p < .001). There was a significant time by group interaction in lnRMSSD (p = .024). Changes were found in the First eleven group from match day +1 to match day +2 (+0.523 ms, p = .003). After the soccer match, there were between-group differences (p < .05) at +24h and +72h in lnRMSSD. Conclusions: During national team training camps, ANS function was only modified 24h and 72h after playing soccer matches, in players who played a minimum of 60 minutes. This knowledge can help coaches to monitor the impact of soccer matches during training camps to detect fatigue and improve recovery.

Predicting Loading Intensity Measuring Velocity in Barbell Hip Thrust Exercise.

ABSTRACT: de Hoyo, M, Núñez, FJ, Sañudo, B, Gonzalo-Skok, O, Muñoz-López, A, Romero-Boza, S, Otero-Esquina, C, Sánchez, H, and Nimphius, S. Predicting loading intensity measuring velocity in barbell hip thrust exercise. J Strength Cond Res 35(8): 2075-2081, 2021-The barbell hip thrust is an increasingly used exercise to target the hip extensors. Direct and indirect measurement of 1 repetition maximum (1RM) to determine the relative load of each exercise is time-consuming; therefore, practitioners may be more in favor of monitoring velocity and determining relative load through velocity-based prediction models for an exercise. This study aimed to assess the relationship between mean velocity (MV) and mean propulsive velocity (MPV) at different relative training loads (%1RM) in the barbell hip thrust exercise. One hundred two male sport science students performed an incremental 1RM testing protocol for the barbell hip thrust exercise, and a linear position transducer measured MV and MPV of the barbell. The 1RM was reached at 0.25 ± 0.03 m·s-1, and the regression model generated to estimate a relative load showed an acceptable standard error of estimate (7.01 ± 1.05% 1RM and 7.36 ± 1.05% 1RM for MV and MPV, respectively) with a very large explained variance (R2 = 0.94). These results may have important practical applications for the prescription and monitoring of the accessory exercise of the hip thrust for monitoring training load and predicting 1RM without undertaking a RM test.

Influence of Strength Level on the Acute Post-Activation Performance Enhancement Following Flywheel and Free Weight Resistance Training.

This study aimed to compare the post-activation potentiation performance enhancement (PAPE) response to the acute inertial flywheel (FW) and free weight resistance training (TRA) on subsequent countermovement jump (CMJ) and sprint performance (10 m sprint). This study used a randomized crossover design including twenty-eight healthy males that were divided into strong (relative one-repetition maximum (1RM) back squat > 2.0 × body mass) and weak (relative 1RM back squat < 2.0 × body mass) groups. All participants performed the following: (a) three reps at 90% of their 1RM back squat (TRA) and (b) three reps on an inertial FW (plus one repetition to initiate flywheel movement) with an intensity that generated a mean propulsive velocity equal to that achieved with 90% of the 1RM back squat. Before and after the conditioning activity, participants performed two CMJs and two 10 m sprints. Within-group analyses showed significantly greater CMJ (d > 0.9, p < 0.001) and sprint performance (d > 0.5, p < 0.05) in the FW and the TRA group. Between-group analysis showed that sprint changes were significantly greater in the FW-strong group when compared with the TRA (F1,18 = 5.11, p = 0.036, η2p = 0.221-large) group. These results suggest that using a squat activation protocol on a FW may lead to an acute positive effect on jump and sprint performance, especially in stronger individuals.

Individual versus team heart rate variability responsiveness analyses in a national soccer team during training camps.

Heart rate variability (HRV) analyses can be performed using group or individual changes. Individual changes could be of potential interest during training camps for national soccer teams. The purpose of this study was to compare whether analysis of individual daily HRV could detect changes in cardiac autonomic responses during training camps for national soccer teams. During two different training camps, 34 professional soccer players were monitored daily over 9 days, using heart rate monitors. Players were divided into First Eleven (those who participated in the main squad) or Reserves. Daily HRV was individually analyzed using a day-to-day method or a baseline (days prior to first match) method, using the smallest worthwhile change and the typical error in the estimate to establish a trivial (random change) zone. Group changes were also analyzed using an ANOVA one-way repeated measures test. Players' responsiveness was classified as High-, Low- or Non-response depending on individual changes. Both analyses showed substantial daily individual changes after playing a soccer match, regardless of the group. However, group changes showed that only First Eleven players had significant changes after playing a soccer match. In conclusion, individual daily HRV analyses are useful in detecting individual changes in professional soccer players.

Is possible an eccentric overload in a rotary inertia device? Comparison of force profile in a cylinder-shaped and a cone-shaped axis devices.

The aims of this study were to compare the force profile of using a horizontal cylinder-shaped axis or a vertical cone-shaped axis to provide resistance in rotary inertia devices, and to report the evolution of kinetic and kinematic variables in experienced athletes during a half-squat exercise. Twenty-two healthy active men participated in the assessment of time, peak velocity, peak force, time to reach the peak force, average force, impulse, and range of movement, during a half-squat incremental test performed on conical inertial device (CP) and on cylinder inertial device (YY). The analysis showed that YY during CON-ECC phased generates substantial higher peak_force, mean_force, impulse, time, and a lower peak_velocity, than CP. We never obtained eccentric overload for peak_force or mean_force. CP offers less resistance to accelerate-decelerate the movement with respect to YY, we need checking whether eccentric overload it is being produced, and the impulse was the only kinetic variable that was able to discriminate between the inertias and devices.

Maximum velocity during loaded countermovement jumps obtained with an accelerometer, linear encoder and force platform: A comparison of technologies.

The maximum velocity (Vmax) reached during countermovement jumps (CMJ) has been considered a performance indicator to evaluate vertical jump ability. The aim of this study was to compare Vmax during loaded CMJ (CMJloaded) using three different technologies to show a criterion for selecting the more appropriate depending on its use. Nine recreationally active men performed a CMJloaded test. Five jumps were made in each of 6 series with a 20- kg barbell + 0, + 5, + 10, + 15, + 20 and + 25 kg, with 2 seconds rest between the jumps and 5 minutes rest between the series to explore a wide range of speeds. Vmax was obtained from force platform, inertial device and linear encoder technologies. Bland-Altman plots and mean differences were used to compare devices. Reproducibility was tested using the intraclass correlation coefficient (ICC) for single measures and typical error (TE). All technologies showed high levels of reproducibility, ICC higher than 0.75 and TE lower than 10 %. There were non-significant differences in Vmax between each pair of technologies (linear encoder 2.11 ±â€¯0.24 m·s-1, accelerometer 2.11 ±â€¯0.26 m·s-1, force platform 2.12 ±â€¯0.24 m·s-1) reporting a very low bias. However the limits of agreement between the different technologies evaluated were high (±â€¯0.33 m·s-1). In conclusion, the accelerometer, linear encoder and force platform were suitably reliable to be used to measure Vmax during loaded vertical jumps but their values were not interchangeable.

Pilot Study Assessing the Influence of Skin Type on the Heart Rate Measurements Obtained by Photoplethysmography with the Apple Watch.

Photoplethysmographic imaging (PPG) is currently used to measure heart rate (HR) and the accuracy of PPG can be influenced by pigmentation of the skin; however, the effects of skin color-related artifacts on PPG during exercise remain unclear. This study aimed to assess the agreement between the Apple Watch photoplethysmography sensor and a criterion, for measuring heart rate across a range of intensities during exercise and to determine the influence of skin type on the accuracy of the measure. Forty-five males (20-43 y) completed the Fitzpatrick Skin Scale and were classified into three different skin type groups: a) types II (n = 15), III (n = 15) and IV (n = 15). Participants performed a graded incremental cycle-ergometer test while simultaneously wearing the Apple Watch and a Polar monitor as a criterion measure. Data from both devices were collected in 5-s epochs. Correlations between devices were very good (0.96-0.99 [95%CI: 0.94 to 0.99]). Significant differences were observed between skin types II and III when the intensity of the exercise was increased, albeit with trivial to small effect sizes (ES: 0.05 to 0.28). All significant differences corresponded to <2% of relative difference between both devices. Bland-Altman analyses showed a trivial but systematic underestimation of HR in the Apple Watch compared to Polar for all skin types during exercise. In conclusion, the Apple Watch accurately measures HR when cycling at different intensities and certain types of skin seem not to influence these measures, which may have important implications for controlling the intensity of exercise.