RESUMEN

We investigated the ecological validity of an inertial measurement unit (IMU) (Vmaxpro) to assess the movement velocity (MV) during a 1-repetition maximum (1RM) test and for the prediction of load-velocity (L-V) variables, as well as the ecological intra- day and inter-day reliability during free-weight bench press (BP) and squat (SQ). Furthermore, we provide recommendations for the practical use of the sensor. Twenty-three strength-trained men completed an incremental 1RM test, whereas seventeen men further participated in another 3 sessions consisting of 3 repetitions with 4 different loads (30, 50, 70 and 90% of 1RM) to assess validity and intra- and inter-day reliability, respectively. The MV was assessed using the Vmaxpro and a 3D motion capture system (MoCap). L-V variables and the 1RM were calculated based on submaximal velocities. The Vmaxpro showed high validity during the 1RM test for BP (r = 0.935) and SQ (r = 0.900), but with decreasing validity at lower MVs. The L-V variables and the 1RM demonstrated high validity for BP (r = 0.808-0.942) and SQ (r = 0.615-0.741) with a systematic overestimation. Coefficients of variance for intra- and inter-day reliability ranged from 2.4% to 9.7% and from 3.2% to 8.6% for BP and SQ, respectively. The Vmaxpro appears valid at high and moderately valid at low MVs. Depending on the required degree of accuracy, the sensor may be sufficient for the prediction of L-V variables and the 1RM. Our data indicate the sensor to be suitable for monitoring changes in MVs within and between training sessions.

RESUMEN

ABSTRACT: Feuerbacher, JF, Jacobs, MW, Dragutinovic, B, Goldmann, J-P, Cheng, S, and Schumann, M. Validity and test-retest reliability of the Vmaxpro sensor for evaluation of movement velocity in the deep squat. J Strength Cond Res 37(1): 35-40, 2023-We aimed at assessing the validity and test-retest reliability of the inertial measurement unit-based Vmaxpro sensor compared with a Vicon 3D motion capture system and the T-Force sensor during an incremental 1-repetition maximum (1RM) test and at submaximal loads. Nineteen subjects reported to the laboratory for the 1RM test sessions, whereas 15 subjects carried out another 3 sessions consisting of 3 repetitions with 4 different intensities (30, 50, 70, and 90% of 1RM) to determine the intra- and interday reliability. The Vmaxpro sensor showed high validity (Vicon: R2 = 0.935; T-Force: R2 = 0.968) but an overestimation of the mean velocities (MVs) of 0.06 ± 0.08 m·s-1 and 0.06 ± 0.06 m·s-1 compared with Vicon and T-Force, respectively. Regression analysis indicated a systematic bias that is increasing with higher MVs. The intraclass correlation coefficients (ICCs) for Vmaxpro were moderate to high for intraday (ICC: 0.662-0.938; p ≤ 0.05) and for interday (ICC: 0.568-0.837; p ≤ 0.05) reliability, respectively. The Vmaxpro is a valid and reliable measurement device that can be used to monitor movement velocities within a training session. However, practitioners should be cautious when assessing movement velocities on separate days because of the moderate interday reliability.

Asunto(s)

RESUMEN

Linear acceleration is a key performance determinant and major training component of many sports. Although extensive research about lower limb kinetics and kinematics is available, consistent definitions of distinctive key body positions, the underlying mechanisms and their related movement strategies are lacking. The aim of this 'Method and Theoretical Perspective' article is to introduce a conceptual framework which classifies the sagittal plane 'shin roll' motion during accelerated sprinting. By emphasising the importance of the shin segment's orientation in space, four distinctive key positions are presented ('shin block', 'touchdown', 'heel lock' and 'propulsion pose'), which are linked by a progressive 'shin roll' motion during swing-stance transition. The shin's downward tilt is driven by three different movement strategies ('shin alignment', 'horizontal ankle rocker' and 'shin drop'). The tilt's optimal amount and timing will contribute to a mechanically efficient acceleration via timely staggered proximal-to-distal power output. Empirical data obtained from athletes of different performance levels and sporting backgrounds are required to verify the feasibility of this concept. The framework presented here should facilitate future biomechanical analyses and may enable coaches and practitioners to develop specific training programs and feedback strategies to provide athletes with a more efficient acceleration technique.

RESUMEN

BACKGROUND: The aim of this study was to examine the impact of personal protective equipment (PPE) on human thermoregulation and its alteration in groups of different training status. METHODS: Forty-five men performed a maximum voluntary contraction test in an upright pull position to determine lower body strength and a graded treadmill test to determine maximum oxygen uptake (V̇O2max). Body composition was estimated via bioelectric impedance analysis. According to specific cutoff values, participants were assigned to a group of endurance-trained, strength-trained, endurance- and strength-trained, or untrained individuals. Subsequently, they completed two graded exercise tests until volitional exhaustion, once wearing sports wear (SPW) and once wearing PPE (20.9 kg). Participants were weighed before and afterward to investigate sweat loss and sweat rate. Body temperature was measured continuously from the tympanic membrane. Energy expenditure was derived from breathing gas analysis. RESULTS: Sweat rate was 91% higher in PPE than in SPW but not significantly different between groups (P>0.05). Body temperature was significantly higher in PPE during submaximal (+1.14±0.45 °C) and maximal exercise intensity (0.68±0.57 °C) and was poorely related to V̇O2max and body composition. Energy expenditure significantly differed between both garments (+37% in PPE) and groups (P<0.05). Additionally, energy expenditure significantly correlated with body weight (r=0.84 in SPW and r=0.68 in PPE). CONCLUSIONS: Strength training alone does not seem to have any or negligible effects on thermoregulation. Endurance training and weight management might lead to rather small improvements in heat tolerance.

Asunto(s)

RESUMEN

The diverse tasks of special operations police (SOP) units place high physical demands on every officer. Being fit for duty requires a wide range of motor abilities which must be trained regularly and in a structured manner. But SOP operators have to plan and manage large proportions of their training alone, which makes it difficult to control. Therefore, this study aimed to highlight strengths and deficits of the SOP operators' fitness by comparing them to elite athletes, and to define future training goals. Retrospective data of 189 male SOP operators were used, who completed several isometric strength tests, a graded exercise test to determine maximal oxygen uptake, and countermovement jumps to determine leg muscle power. On the basis of a literature search, performance data were then compared to a total of 3,028 elite male athletes from 36 Summer Olympic disciplines. Pooled means and standard deviations were calculated for each discipline and effect sizes were used to analyze their similarities and differences to the SOP unit. On average, SOP operators were taller, heavier, and stronger than elite athletes. But both the ability to convert this strength into explosive movement and aerobic power was significantly less developed. From this point of view, SOP operators should consider polarized endurance training to work efficiently on improving aerobic performance. In addition, regular plyometric training seems necessary to improve leg muscle power and agility.

RESUMEN

PURPOSE: To investigate the influence of aerobic capacity, muscle strength, and body composition on performance and metabolic demands of men wearing personal protective equipment (PPE). METHODS: 45 men were assigned to one of four groups which significantly differed in upright pull isometric strength (MVC ≤ 1325 N or ≥ 1531 N) and maximum oxygen uptake (VO2max ≤ 51.9 mL min-1·kg-1 or ≥ 56.0 mL min-1·kg-1): endurance-trained (low MVC, high VO2max), strength-trained (high MVC, low VO2max), endurance- and strength-trained (high MVC, high VO2max), and untrained (low MVC, low VO2max). Each participant underwent two test series consisting of a repeated 10 m dummy drag and a graded exercise test wearing either sportswear or PPE of a German riot police unit weighing 20.9 kg (statistics: two-way repeated measures ANOVA, stepwise multiple linear regressions). RESULTS: With PPE, dummy drag and running performance were impaired by 14 ± 9% and 58 ± 7%. Groups with high MVC dragged the dummy significantly faster than groups with low MVC (17.5 ± 1.8 s/17.6 ± 1.4 s vs. 23.4 ± 5.6 s/22.3 ± 3.5 s). Running distance was significantly higher in groups with high VO2max (4.5 ± 0.8 km/4.4 ± 0.7 km vs. 3.1 ± 0.5 km/2.8 ± 0.5 km). Body composition variables partially correlated with performance (R ranging from -0.70 to 0.41), but were not significant predictors of the regression models in PPE. CONCLUSIONS: Individuals who showed a certain degree of aerobic endurance, as well as muscle strength, performed consistently well during the test series. Therefore, none of these variables should be trained in isolation but optimized in combination to be capable in a variety of operational tasks.

Asunto(s)

RESUMEN

The purpose of this study was to validate the calculation of reaction time (RT) and normalised power in block starts without considering arm ground reaction forces (GRFs) or using two kinematics-only methods. The RT and normalised power in the action phase were calculated using four different methods: using GRFs of arms and legs by force plates (whole F-based method), which can be regarded as the most valid method, using GRFs of legs captured by force plates (legs F-based method), using position of the centre of mass of the entire body captured by high-speed cameras (whole P-based method), and using only a partial subset of segment position (partial P-based method). Bland-Altman plots demonstrated that the RT of the legs F-based method was not similar to that of the whole F-based method: the mean difference was 7.4 ms and the 95% limits of agreement was-45.1 to 59.8 ms, and it was the least valid method for the calculation among the four methods. In contrast, the normalised power was more valid in the legs F-based method, followed by whole and partial P-based methods. This information will help researchers and practitioners to decide upon their analysis methods when analysing block start performance.

Asunto(s)

RESUMEN

Wahl, P, Sanno, M, Ellenberg, K, Frick, H, Böhm, E, Haiduck, B, Goldmann, J-P, Achtzehn, S, Brüggemann, G-P, Mester, J, and Bloch, W. Aqua cycling does not affect recovery of performance, damage markers, and sensation of pain. J Strength Cond Res 31(1): 162-170, 2017-To examine the effects of aqua cycling (AC) vs. passive recovery (P) on performance, markers of muscle damage, delayed onset of muscle soreness (DOMS), and the persons perceived physical state (PEPS) after 300 countermovement jumps (CMJs). Twenty male participants completed 300 CMJs. Afterward, they were randomly assigned to either the P group or the AC group, the latter performing 30 minutes of AC. Before, directly after the 300 CMJs, after the recovery session, and up to 72 hours post, performance of leg extensor muscles, damage markers, the PEPS, and DOMS were measured. Jumping height during 300 CMJs significantly decreased in both groups (AC: 13.4% and P: 14.6%). Maximal isometric strength (AC: 21% and P: 22%) and dynamic fatigue test (AC: 35% and P: 39%) of leg extensor muscles showed significant decreases in both groups. Myoglobin, creatine kinase, and lactate dehydrogenase significantly increased over time in both groups. Each of the 4 dimensions of the PEPS and DOMS showed significant changes over time. However, no significant differences between both groups were found for any of the parameters. Coaches and athletes should be aware that vertical jumping-induced fatigue decreases the ability to generate maximal isometric and submaximal dynamic force for more than 3 days after training. A single 30-minute session of AC was not able to attenuate the effects on muscular performance, markers of muscle damage, DOMS, or the PEPS compared with passive rest.

Asunto(s)

RESUMEN

The purpose of this study was to explore the relationship between the forces applied to the starting blocks and the start performances (SPs) of amputee sprinters (ASs) and non-amputee sprinters (NASs). SPs of 154 male and female NASs (100-m personal records [PRs], 9.58-14.00 s) and 7 male ASs (3 unilateral above knee, 3 unilateral below knee, 1 bilateral below knee; 100 m PRs, 11.70-12.70 s) with running specific prostheses (RSPs) were analysed during full-effort sprint starts using instrumented starting blocks that measured the applied forces in 3D. Using the NAS dataset and a combination of factor analysis and multiple regression techniques, we explored the relationship between force characteristics and SP (quantified by normalized average horizontal block power). Start kinetics were subsequently compared between ASs and NASs who were matched based on their absolute 100 m PR and their 100 m PR relative to the world record in their starting class. In NASs, 86% of the variance in SP was shared with five latent factors on which measured parameters related to force application to the rear and front blocks and the respective push-off directions in the sagittal plane of motion were loaded. Mediolateral force application had little influence on SP. The SP of ASs was significantly reduced compared to that of NASs matched on the basis of relative 100-m PR (-33.8%; d = 2.11, p < 0.001), while a non-significant performance reduction was observed when absolute 100-m PRs were used (-17.7%; d = 0.79, p = 0.09). These results are at least partially explained by the fact that force application to the rear block was clearly impaired in the affected legs of ASs.

Asunto(s)

RESUMEN

OBJECTIVES: Short-term exposure (2?30 seconds) to segmental mechanical vibrations with frequencies between 20 and 80 Hz affects proprioception of the central nervous system and manual dexterity and strength of man. It could be supposed that during fast-roping, Soldiers are exposed to hand?arm vibrations caused by the geometry of the rope. After the maneuver, Soldiers are encouraged to operate with high precision (e.g., aiming and shooting) within a few seconds. For safety, disturbances of the sensory system should be strongly avoided. The purpose of the study was to determine the vibrations induced by different rope geometries during fast-roping. METHODS: Eight men of the German Special Forces performed 10 fast-roping maneuvers with two different shaped ropes (slightly molded versus deeply molded). Vibration data and frequency spectrum for each trial were measured by using fast Fourier transformation. RESULTS: The analysis of data showed that fast-roping with a slightly molded rope produced frequencies of up to 10 Hz, while the frequencies with a deeply molded rope accounted for 18 to 60 Hz. The ropes differed significantly (p<.001) in frequencies between 20 and 50 Hz. The exposure time of vibration lasted between 3 and 5 seconds. CONCLUSION: Considering the negative effects associated with vibrations, prudence is required when using deeply molded ropes due to the increased vibrations of about 20 Hz.

Asunto(s)

RESUMEN

The purpose of the present study was to investigate whether altered longitudinal bending stiffness (LBS) levels of the midsole of a running shoe lead to a systematic change in lower extremity joint lever arms of the ground reaction force (GRF). Joint moments and GRF lever arms in the sagittal plane were determined from 19 male subjects running at 3.5 m/s using inverse dynamics procedures. LBS was manipulated using carbon fiber insoles of 1.9 mm and 3.2 mm thickness. Increasing LBS led to a significant shift of joint lever arms to a more anterior position. Effects were more pronounced at distal joints. Ankle joint moments were not significantly increased in the presence of higher GRF lever arms when averaged over all subjects. Still, two individual strategies (1: increase ankle joint moments while keeping push-off times almost constant, 2: decrease ankle joint moments and increase push-off times) could be identified in response to increased ankle joint lever arms that might reflect individual differences between subjects with respect to strength capacities or anthropometric characteristics. The results of the present study indicate that LBS systematically influences GRF lever arms of lower extremity joints during the push-off phase in running. Further, individual responses to altered LBS levels could be identified that could aid in finding optimum LBS values for a given individual.

Asunto(s)

RESUMEN

The metatarsal phalangeal joint (MPJ) and its crossing toe flexor muscles (TFM) represent the link between the large energy generating leg extensor muscles and the ground. The purpose of this study was to examine the functional adaptability of TFM to increased mechanical stimuli and the effects on walking, running and jumping performance. Fifteen men performed a heavy resistance TFM strength training with 90% of the maximal voluntary isometric contraction (MVIC) for 7 weeks (560 contractions) for the left and right foot. Maximal MPJ and ankle plantar flexion moments during MVICs were measured in dynamometers before and after the intervention. Motion analyses (inverse dynamics) were performed during barefoot walking, running, and vertical and horizontal jumping. Athletic performance was determined by measuring jump height and distance. Left (0.21 to 0.38 Nm · kg(-1); P < 0.001) and right (0.24 to 0.40 Nm · kg(-1); P < 0.001) MPJ plantar flexion moments in the dynamometer, external MPJ dorsiflexion moments (0.69 to 0.75 Nm · kg(-1); P = 0.012) and jump distance (2.25 to 2.31 m; P = 0.006) in horizontal jumping increased significantly. TFM responded highly to increased loading within a few weeks. The increased force potential made a contribution to an athlete's performance enhancement.

Asunto(s)

RESUMEN

The maximal force a muscle produces depends among others on the length of the muscle and therefore on the positions of the joints the muscle crosses. Long and short toe flexor muscles (TFM) cross the ankle joints and metatarsal phalangeal joints (MPJ) and work against gravity during human locomotion. The purpose of this study was to describe the maximal moments around the MPJ during maximal voluntary isometric contractions (MVIC) of the TFM as a function of ankle joint and MPJ position. Twenty men performed MVIC of the TFM in a custom-made dynamometer. Ankle and MPJ angles were modified after each contraction. External moments of force around the MPJ were determined. Moments ranged between 6.3 ± 2.6 Nm and 14.2 ± 5.8 Nm. Highest moments were produced at 0°-10° ankle joint dorsal flexion and 25°-45° MPJ dorsal flexion. Lowest moments were generated at 35° ankle joint plantar flexion and 0° MPJ dorsal flexion. In conclusion, if the ankle is plantar-flexed, dorsal flexion of the MPJ avoids a disadvantage of the force-length relationship of TFM. Therefore, MPJ dorsal flexion is a necessary function in the push-off phase of human locomotion to work against the loss of the mechanical output at the forefoot caused by plantar flexion of the ankle.

Asunto(s)

RESUMEN

The purpose of this study was to investigate whether sprint performance is related to lower leg musculoskeletal geometry within a homogeneous group of highly trained 100-m sprinters. Using a cluster analysis, eighteen male sprinters were divided into two groups based on their personal best (fast: N=11, 10.30±0.07s; slow: N=7, 10.70±0.08s). Calf muscular fascicle arrangement and Achilles tendon moment arms (calculated by the gradient of tendon excursion versus ankle joint angle) were analyzed for each athlete using ultrasonography. Achilles tendon moment arm, foot and ankle skeletal geometry, fascicle arrangement as well as the ratio of fascicle length to Achilles tendon moment arm showed no significant (p>0.05) correlation with sprint performance, nor were there any differences in the analyzed musculoskeletal parameters between the fast and slow sprinter group. Our findings provide evidence that differences in sprint ability in world-class athletes are not a result of differences in the geometrical design of the lower leg even when considering both skeletal and muscular components.

Asunto(s)