Energetics and Basic Stroke Kinematics of Swimming With Different Styles of Wetsuits.

ABSTRACT: Lim, B, Villalobos, A, Mercer, JA, and Crocker, GH. Energetics and basic stroke kinematics of swimming with different styles of wetsuits. J Strength Cond Res XX(X): 000-000, 2024-This study investigated the physiological responses and basic stroke kinematics while wearing different styles of wetsuits during submaximal intensity front-crawl swimming. Fourteen subjects (6 men and 8 women) completed a swimming-graded exercise test to determine maximal aerobic capacity (V̇O2max) and four 4-minute submaximal front-crawl swims at a pace that elicited 80% of V̇O2max with different wetsuits: regular swimsuit (no wetsuit [NWS]), buoyancy shorts (BS), sleeveless wetsuit (SLW), and full-sleeve wetsuit (FSW). The rate of oxygen consumption (V̇O2), rate of carbon dioxide production (V̇CO2), minute ventilation (V̇E), heart rate (HR), respiratory exchange ratio, and cost of swimming (CS) were determined as the average for the last minute of each trial. The rating of perceived exertion was assessed after each swimming bout. In addition, stroke length and index were determined from swimming pace and stroke rate. V̇O2, V̇CO2, V̇E, HR, and CS differed significantly among wetsuit conditions (p < 0.01). Respiratory exchange ratio and rating of perceived exertion also varied by wetsuit conditions (p < 0.05). However, stroke rate, length, and index were not significantly different across wetsuit conditions (p > 0.05). No differences existed between SLW and FSW for any dependent variable (p > 0.05). Results from this study suggest that swimming at the same pace without a wetsuit is the least economical, and both SLW and FSW are most and equally economical without significant kinematic changes. In addition, BS could be beneficial during training and racing in terms of less physiological demands than a regular swimsuit but not as economical as the SLW or FSW.

Myosin Vb mobilizes recycling endosomes and AMPA receptors for postsynaptic plasticity.

Learning-related plasticity at excitatory synapses in the mammalian brain requires the trafficking of AMPA receptors and the growth of dendritic spines. However, the mechanisms that couple plasticity stimuli to the trafficking of postsynaptic cargo are poorly understood. Here we demonstrate that myosin Vb (MyoVb), a Ca2+-sensitive motor, conducts spine trafficking during long-term potentiation (LTP) of synaptic strength. Upon activation of NMDA receptors and corresponding Ca2+ influx, MyoVb associates with recycling endosomes (REs), triggering rapid spine recruitment of endosomes and local exocytosis in spines. Disruption of MyoVb or its interaction with the RE adaptor Rab11-FIP2 abolishes LTP-induced exocytosis from REs and prevents both AMPA receptor insertion and spine growth. Furthermore, induction of tight binding of MyoVb to actin using an acute chemical genetic strategy eradicates LTP in hippocampal slices. Thus, Ca2+-activated MyoVb captures and mobilizes REs for AMPA receptor insertion and spine growth, providing a mechanistic link between the induction and expression of postsynaptic plasticity.

The effects of stride frequency manipulation on physiological and perceptual responses during backward and forward running with body weight support.

PURPOSE: We investigated the influence of a change in stride frequency on physiological and perceptual responses during forward and backward running at different body weight support (BWS) levels. METHODS: Participants ran forward and backward at 0% BWS, 20% BWS, and 50% BWS conditions on a lower body positive pressure treadmill. The stride frequency conditions consisted of forward and backward running at preferred stride frequency (PSF), PSF + 10%, and PSF-10%. We measured oxygen uptake ([Formula: see text]O2), carbon dioxide production, heart rate (HR), muscle activity from the lower extremity, and rating of perceived exertion (RPE). Furthermore, we calculated the metabolic cost of transport (CoT). RESULTS: [Formula: see text]O2, HR, CoT, and muscle activity from the rectus femoris were significantly different between stride frequency conditions (P < 0.05). [Formula: see text]O2, HR, and CoT during running at PSF + 10% were significantly higher than when running at PSF, regardless of running direction and BWS (P < 0.05). However, RPE was not different between stride frequency conditions (P > 0.05: e.g., 12.8-13.8 rankings in RPE for backward running at 0% BWS). CONCLUSIONS: Manipulation of stride frequency during running may have a greater impact on physiological responses than on perceptual responses at a given speed, regardless of running direction and BWS. Individuals who need to increase their physiological demands during running may benefit from a 10% increase in stride frequency from the PSF, regardless of BWS and running direction.

Molecular mechanisms and structural features of cardiomyopathy-causing troponin T mutants in the tropomyosin overlap region.

Point mutations in genes encoding sarcomeric proteins are the leading cause of inherited primary cardiomyopathies. Among them are mutations in the TNNT2 gene that encodes cardiac troponin T (TnT). These mutations are clustered in the tropomyosin (Tm) binding region of TnT, TNT1 (residues 80-180). To understand the mechanistic changes caused by pathogenic mutations in the TNT1 region, six hypertrophic cardiomyopathy (HCM) and two dilated cardiomyopathy (DCM) mutants were studied by biochemical approaches. Binding assays in the absence and presence of actin revealed changes in the affinity of some, but not all, TnT mutants for Tm relative to WT TnT. HCM mutants were hypersensitive and DCM mutants were hyposensitive to Ca2+ in regulated actomyosin ATPase activities. To gain better insight into the disease mechanism, we modeled the structure of TNT1 and its interactions with Tm. The stability predictions made by the model correlated well with the affinity changes observed in vitro of TnT mutants for Tm. The changes in Ca2+ sensitivity showed a strong correlation with the changes in binding affinity. We suggest the primary reason by which these TNNT2 mutations between residues 92 and 144 cause cardiomyopathy is by changing the affinity of TnT for Tm within the TNT1 region.

Metabolic Costs During Backward Running with Body Weight Support.

We investigated metabolic costs, rating of perceived exertion (RPE), stride frequency (SF), and preferred speed (PS) during forward and backward running at different levels of body weight support (BWS). Participants completed forward and backward running on a lower body positive pressure treadmill at their preferred speed for forward and backward running at 0%BWS, 20%BWS, and 50%BWS. Oxygen uptake (V̇O2), heart rate (HR), RPE, SF, and PS were measured. HR, RPE, and SF during forward and backward running decreased with increasing BWS (P<0.05).V̇O2 during both forward and backward running at 50%BWS was significantly lower than when running at 0%BWS (P<0.01). However, PS during forward and backward running increased with increasing BWS (P<0.01). Furthermore,V̇O2 was different between running directions only when running at 0%BWS (P<0.01). HR and RPE were not different between running directions (P>0.05). SF during backward running was higher than that of forward running (P<0.01). PS during backward running was lower than when running forward (P<0.001). Our observations suggest that individuals may select PS and SF during running with BWS in a way that resulted in similar metabolic costs, regardless of direction of locomotion.

Relationships Between Countermovement Jump Ground Reaction Forces and Jump Height, Reactive Strength Index, and Jump Time.

Barker, LA, Harry, JR, and Mercer, JA. Relationships between countermovement jump ground reaction forces and jump height, reactive strength index, and jump time. J Strength Cond Res 32(1): 248-254, 2018-The purpose of this study was to determine the relationship between ground reaction force (GRF) variables to jump height, jump time, and the reactive strength index (RSI). Twenty-six, Division-I, male, soccer players performed 3 maximum effort countermovement jumps (CMJs) on a dual-force platform system that measured 3-dimensional kinetic data. The trial producing peak jump height was used for analysis. Vertical GRF (Fz) variables were divided into unloading, eccentric, amortization, and concentric phases and correlated with jump height, RSI (RSI = jump height/jump time), and jump time (from start to takeoff). Significant correlations were observed between jump height and RSI, concentric kinetic energy, peak power, concentric work, and concentric displacement. Significant correlations were observed between RSI and jump time, peak power, unload Fz, eccentric work, eccentric rate of force development (RFD), amortization Fz, amortization time, second Fz peak, average concentric Fz, and concentric displacement. Significant correlations were observed between jump time and unload Fz, eccentric work, eccentric RFD, amortization Fz, amortization time, average concentric Fz, and concentric work. In conclusion, jump height correlated with variables derived from the concentric phase only (work, power, and displacement), whereas Fz variables from the unloading, eccentric, amortization, and concentric phases correlated highly with RSI and jump time. These observations demonstrate the importance of countermovement Fz characteristics for time-sensitive CMJ performance measures. Researchers and practitioners should include RSI and jump time with jump height to improve their assessment of jump performance.

Muscle Activity and Physiological Responses During Running in Water and on Dry Land at Submaximal and Maximal Efforts.

Masumoto, K, Mefferd, KC, Iyo, R, and Mercer, JA. Muscle activity and physiological responses during running in water and on dry land at submaximal and maximal efforts. J Strength Cond Res 32(7): 1960-1967, 2018-We investigated muscle activity, oxygen uptake, heart rate, and rating of perceived exertion during running in water and on dry land at submaximal and maximal efforts. Eleven recreational runners performed deep-water running (DWR) and treadmill running (TMR) graded exercise tests on separate days. On the third-test day, the subjects exercised at their 60, 80, and 100% of maximal oxygen uptake (V[Combining Dot Above]O2max) by matching specific stride frequencies or running speeds. V[Combining Dot Above]O2max, maximal heart rate (HRmax), and rating of perceived exertion at maximal effort (RPEmax) were measured. Furthermore, muscle activity from the rectus femoris, biceps femoris, tibialis anterior, and gastrocnemius were measured. V[Combining Dot Above]O2max (DWR: 48.9 ± 5.7 ml·kg·min; TMR: 59.2 ± 5.6 ml·kg·min; p < 0.001) and HRmax (DWR: 174.1 ± 9.6 beats·min; TMR: 191.2 ± 6.9 beats·min; p < 0.001) were each lower during DWR vs. TMR. In addition, RPEmax was not significantly different between DWR and TMR (DWR: 17.8 ± 1.9; TMR: 18.4 ± 1.3; p > 0.05). Furthermore, muscle activity from all tested muscles was not influenced by the interaction of mode and intensity (p > 0.05). Muscle activity from all tested muscles was different between modes (p < 0.05) and between intensities (p < 0.001). Specifically, muscle activity from the tested muscles during DWR was 29-69% lower than that of TMR at maximal effort. Athletes and coaches should consider that the exercise intensity during DWR can be overestimated, if exercise prescription was made according to the maximal responses during TMR.

Bilateral Comparison of Vertical Jump Landings and Step-off Landings From Equal Heights.

Harry, JR, Silvernail, JF, Mercer, JA, and Dufek, JS. Bilateral comparison of vertical jump landings and step-off landings from equal heights. J Strength Cond Res 32(7): 1937-1947, 2018-The purpose of this investigation was to examine kinetic, kinematic, and temporal parameters during vertical jump landings (VJL) and step-off landings (STL) from equal heights. Five men (25.0 ± 1.6 years; 1.7 ± 0.4 m; 79.7 ± 7.1 kg) and 5 women (20.8 ± 1.6 years; 1.6 ± 0.4 m; 68.5 ± 7.1 kg) performed 15 VJL and 15 STL. Paired-samples t-tests (α = 0.05) compared impact velocity and the times to the first (F1) and second (F2) peak vertical ground reaction force magnitudes (tF1 and tF2) and the end of impact. Two-way analyses of variance (α = 0.05) compared limb and task differences in F1, F2, hip, knee, and ankle joint angles at ground contact, F1, F2, and the end of impact, and hip, knee, and ankle joint displacements between contact and F1, F1 and F2, and F2 and the end of impact. Impact velocity was not different between STL and VJL, although STL produced a greater F1 and a more rapid tF2. Greater hip, knee, and ankle flexion/dorsiflexion occurred during STL throughout the majority of impact regardless of limb. Lesser hip, knee, and ankle joint displacements occurred during STL regardless of limb between F1 and F2, whereas greater joint displacement occurred between F2 and the end of impact. Lastly, knee joint angles at ground contact differed between limbs during STL only. Strength and conditioning professionals aiming to improve an athlete's performance during sport-specific jump landings should consider the likely impact attenuation outcomes before selecting STL or VJL in training.

Vertical and Horizontal Impact Force Comparison During Jump Landings With and Without Rotation in NCAA Division I Male Soccer Players.

Harry, JR, Barker, LA, Mercer, JA, and Dufek, JS. Vertical and horizontal impact force comparison during jump landings with and without rotation in NCAA Division I male soccer players. J Strength Cond Res 31(7): 1780-1786, 2017-There is a wealth of research on impact force characteristics when landing from a jump. However, there are no data on impact forces during landing from a jump with an airborne rotation about the vertical axis. We examined impact force parameters in the vertical and horizontal axes during vertical jump (VJ) landings and VJ landings with a 180° rotation (VJR). Twenty-four Division I male soccer players performed 3 VJ and VJR landings on a dual-force platform system. Paired-samples t-tests (α = 0.05) compared differences in the first (F1) and second (F2) peak vertical ground reaction forces, times to F1 (tF1), F2 (tF2), and the end of the impact phase, vertical impulse, and anterior-posterior and medial-lateral force couples. Effect sizes (ES; large >0.8) were computed to determine the magnitude of the differences. Lower jump height (41.60 ± 4.03 cm, VJ landings; 39.40 ± 4.05 cm, VJR landings; p = 0.002; ES = 0.39), greater F2 (55.71 ± 11.95 N·kg, VJ; 68.16 ± 14.82 N·kg; p < 0.001; ES = 0.94), faster tF2 (0.057 ± 0.012 seconds, VJ; 0.047 ± 0.011 seconds, VJR; p = 0.001; ES = 0.89), greater anterior-posterior (0.06 ± 0.03 N·s·kg, VJ; 0.56 ± 0.15 N·s·kg, VJR; p < 0.001; ES = 1.83) and medial-lateral force couples (0.29 ± 0.11 N·s·kg, VJ; 0.56 ± 0.14 N·s·kg, VJR; p < 0.001; ES = 1.46) occurred during VJR landings. No other differences were identified. This kinetic analysis determined that landing from a jump with 180° airborne rotation is different than landing from a jump without an airborne rotation. Male Division I soccer players could benefit from increasing the volume of VJR landings during training to address the differences in jump height and force parameters compared with VJ landings.

Aerial Rotation Effects on Vertical Jump Performance Among Highly Skilled Collegiate Soccer Players.

Barker, LA, Harry, JR, Dufek, JS, and Mercer, JA. Aerial rotation effects on vertical jump performance among highly skilled collegiate soccer players. J Strength Cond Res 31(4): 932-938, 2017-In soccer matches, jumps involving rotations occur when attempting to head the ball for a shot or pass from set pieces, such as corner kicks, goal kicks, and lob passes. However, the 3-dimensional ground reaction forces used to perform rotational jumping tasks are currently unknown. Therefore, the purpose of this study was to compare bilateral, 3-dimensional, and ground reaction forces of a standard countermovement jump (CMJ0) with those of a countermovement jump with a 180° rotation (CMJ180) among Division-1 soccer players. Twenty-four participants from the soccer team of the University of Nevada performed 3 trials of CMJ0 and CMJ180. Dependent variables included jump height, downward and upward phase times, vertical (Fz) peak force and net impulse relative to mass, and medial-lateral and anterior-posterior force couple values. Statistical significance was set a priori at α = 0.05. CMJ180 reduced jump height, increased the anterior-posterior force couple in the downward and upward phases, and increased upward peak Fz (p ≤ 0.05). All other variables were not significantly different between groups (p > 0.05). However, we did recognize that downward peak Fz trended lower in the CMJ0 condition (p = 0.059), and upward net impulse trended higher in the CMJ0 condition (p = 0.071). It was concluded that jump height was reduced during the rotational jumping task, and rotation occurred primarily via AP ground reaction forces through the entire countermovement jump. Coaches and athletes may consider additional rotational jumping in their training programs to mediate performance decrements during rotational jump tasks.

Mechanistic heterogeneity in contractile properties of α-tropomyosin (TPM1) mutants associated with inherited cardiomyopathies.

The most frequent known causes of primary cardiomyopathies are mutations in the genes encoding sarcomeric proteins. Among those are 30 single-residue mutations in TPM1, the gene encoding α-tropomyosin. We examined seven mutant tropomyosins, E62Q, D84N, I172T, L185R, S215L, D230N, and M281T, that were chosen based on their clinical severity and locations along the molecule. The goal of our study was to determine how the biochemical characteristics of each of these mutant proteins are altered, which in turn could provide a structural rationale for treatment of the cardiomyopathies they produce. Measurements of Ca(2+) sensitivity of human ß-cardiac myosin ATPase activity are consistent with the hypothesis that hypertrophic cardiomyopathies are hypersensitive to Ca(2+) activation, and dilated cardiomyopathies are hyposensitive. We also report correlations between ATPase activity at maximum Ca(2+) concentrations and conformational changes in TnC measured using a fluorescent probe, which provide evidence that different substitutions perturb the structure of the regulatory complex in different ways. Moreover, we observed changes in protein stability and protein-protein interactions in these mutants. Our results suggest multiple mechanistic pathways to hypertrophic and dilated cardiomyopathies. Finally, we examined a computationally designed mutant, E181K, that is hypersensitive, confirming predictions derived from in silico structural analysis.

Determining if muscle activity is related to preferred stride frequency during running in the water and on land.

PURPOSE: To determine if muscle activity is related to preferred stride frequency (PSF) during deep water running (DWR) and treadmill running on dry land (TMR). METHODS: Subjects (n = 11; 26.2 ± 4.4 years) completed TMR and DWR at their mode-specific preferred stride frequency (PSF mode). They also ran at stride frequencies which were lower and higher than the PSF mode (i.e., PSF mode ± 5, 10, and 15 %). Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GL), SF, and rating of perceived exertion (RPE) were measured. RESULTS: The PSF mode during DWR was significantly lower than that of TMR (i.e., 49.9 ± 11.0 versus 81.9 ± 4.8 strides/min, P < 0.0001). Additionally, muscle activity from the RF, TA, and GL during DWR was significantly lower than during TMR at respective PSF mode (~83.6 % decrease, P < 0.0001). However, RPE while running at the PSF mode during DWR and TMR was similar. During DWR, the RF, TA, and GL muscle activity was not different between PSF mode and any other SF conditions (P > 0.0005). During TMR, there was no significant difference in the RF and GL muscle activity between PSF mode and any other SF conditions during TMR (P > 0.0005). CONCLUSIONS: During DWR, subjects selected a lower PSF than during TMR even though RPE was the same. It was also determined that the relationship between muscle activity and changes in SF relative to the PSF mode was unique during DWR and TMR.

Heel-toe running: A new look at the influence of foot strike pattern on impact force.

BACKGROUND/OBJECTIVE: It is important to understand the factors that influence the impact force observed during running, since the impact force is likely to be related to overuse injuries. The purpose of this study was to compare the impact force during running when participants were instructed to use different foot strike patterns: obvious heel strike (Obvious-HS), subtle heel strike (Subtle-HS), midfoot strike (Mid-FS), and fore foot strike (Fore-FS) patterns. METHODS: Participants (n = 10, 25 ± 5.7 years, 70.2 ± 12.1 kg, 174.6 ± 7.2 cm) completed four foot strike patterns while running over ground: Obvious-HS, Subtle-HS, Mid-FS, and Fore-FS. Speed was controlled between conditions (random order). Vertical ground reaction forces were recorded (1000 Hz) along with the impact force, peak force, and stance time for analysis. A repeated measures analysis of variance was used to compare each variable across foot strike instructions, with post hoc comparisons contrasting Obvious-HS to each of the other conditions. RESULTS: Impact force was influenced by foot strike instructions, with Obvious-HS being greater than Subtle-HS and Fore-FS (p < 0.05) but not different from Mid-FS (p > 0.05). The peak force was not influenced by foot strike instructions (p > 0.05); stance time was longer during Obvious-HS than during Mid-FS or Fore-FS (p < 0.05), but not different from Subtle-HS (p > 0.05). CONCLUSION: The unique observation of this study was that impact force was different when participants were instructed to run with either an Obvious-HS or a Subtle-HS at contact. Both these foot strike patterns would have been considered rear foot strike patterns, suggesting that something other than which specific part of the foot strikes the ground initially influenced impact force.

Muscle activity during running with different body-weight-support mechanisms: aquatic environment versus body-weight-support treadmill.

BACKGROUND: Body-weight (BW) support during running can be accomplished using deep-water running (DWR; 100% BW support) and a lower-body positive-pressure (LBPP) treadmill. PURPOSE: To compare lower-extremity muscle activity during DWR and running on an LBPP treadmill at matched stride frequency. METHODS: Eight subjects (40 ± 6.5 y, 173 ± 7.2 cm, 66.9 ± 11.7 kg) completed 4 running conditions all at a preferred stride frequency that was determined while running with no support. Two conditions were running on the LBPP treadmill at 60% and 80% of BW, and the other 2 conditions were different DWR styles: high knee (DWR-HK) and cross-country (DWR-CC). Average (AVG) and root-mean-square (RMS) electromyography (rectus femoris, biceps femoris, gastrocnemius, and tibialis anterior) were each compared among conditions (repeated-measures analysis of variance). RESULTS: Results for AVG and RMS variables were identical for statistical tests for each muscle. Rectus femoris electromyography during DWR-HK was lower than that of DWR-CC (P < .05) but not different than either 60% BW or 80% BW (P > .05). Biceps femoris electromyography was less during DWR-HK than DWR-CC (P < .05) but greater during DWR-HK than either BW 60% or BW 80% (P < .05). Neither gastrocnemius nor tibialis anterior electromyography differed between conditions (P > .05). CONCLUSION: Neither the mechanism of BW support nor style of DWR influenced gastrocnemius or tibialis anterior muscle activity during running at the same stride frequency. However, rectus femoris and biceps femoris muscle activity were influenced by not only the mechanism of BW support but also the style of DWR.

Muscle activity while running at 20%-50% of normal body weight.

Little information exists on how body weight (BW) support influences running biomechanics. The study aim was to determine how reducing BW by 50%-80% influences muscle activity while running at different speeds. Subjects (n = 7) ran at 100%, 115%, 125% of preferred speed at 100%, 50%, 40%, 30%, 20% of BW per speed. Average (AVG) electromyography of the rectified signal was compared (within subject design; 3-speeds × 5-BW, repeated measures ANOVAs; biceps femoris [BF], rectus femoris [RF], tibialis anterior [TA], gastrocnemius [GA]). RF, BF, and GA AVG were not influenced by BW-speed interaction (p > .05) and increased across speeds (p < .05). RF and GA AVG signal was reduced as BW was reduced (p < .05), but BF only tended to be different (p = .08). TA was influenced by BW-speed interaction (p < .05) with EMG decreasing across BW (p < .05) while increasing across speeds except at 100% BW. Overall, muscle activity increased with speed and decreased by BW reductions.

The combined influence of body weight support and running direction on self-selected movement patterns.

We investigated metabolic costs, muscle activity, and perceptual responses during forward and backward running at matched speeds at different body weight support (BWS) conditions. Participants ran forward and backward on a lower body positive pressure treadmill at 0%BWS, 20%BWS, and 50%BWS conditions. We measured oxygen uptake, carbon dioxide production, heart rate, muscle activity, and stride frequency. Additionally, we calculated metabolic cost of transport. Furthermore, we used rating of perceived exertion and feeling scale to investigate perceptual responses. Feeling scale during running was higher with increasing BWS (0-50%BWS), regardless of running direction (p < 0.05). Oxygen uptake, heart rate, and metabolic cost of transport were influenced by the interaction of running direction and BWS (p < 0.01). For example, metabolic cost of transport during backward running was greater than when running forward only when running at 0%BWS (i.e., 4.4 ± 1.1 and 5.8 ± 1.4 J/kg/m for forward and backward running, respectively: p < 0.001). However, rectus femoris muscle activity, stride frequency, and rating of perceived exertion during backward running were averages of 113.5%, 11.3%, and 2.8 rankings greater than when running forward, respectively, regardless of BWS (p < 0.001). We interpret our observations to indicate that environment (in the context of effective body weight) is a critical factor that determines self-selected movement patterns during forward and backward running.

Influence of speed on running strategies during forward and backward running with body weight support.

BACKGROUND: Running with body weight support (BWS) and backward running have been included in exercise programs. However, it is not known how running characteristics of forward and backward running with BWS are influenced by the deviation in the running speed from the preferred speed (PS). The purpose of this study was to investigate how metabolic cost, muscle activity, and perceptual responses of forward and backward running with BWS are influenced by the deviation in running speed from the PS. METHODS: Eleven participants ran forward and backward at 0%BWS, 20%BWS, and 50%BWS conditions. The running speed conditions were set to their mode-specific PS, PS+10%, and PS-10%. We measured metabolic cost, muscle activity, stride frequency, rating of perceived exertion, and feeling scale. RESULTS: Metabolic cost, muscle activity (rectus femoris and gastrocnemius), and rating of perceived of exertion during running increased with increasing speed, regardless BWS and running direction (P<0.05). For example, a 10% increase in running speed from the PS produced averages of 7.1% and 7.7% increases in oxygen uptake and rectus femoris muscle activity, respectively. However, stride frequency during forward and backward running with BWS did not increase with increasing speed when running speed was manipulated around the PS (i.e., 10% increments: P>0.05), with the exception of forward running at 50%BWS. CONCLUSIONS: A 10% increase in running speed from the PS may be useful for individuals who are required to increase their metabolic cost, muscle activity, and perceptual responses during running, regardless of BWS and running direction.

Shoulder Muscle Activity While Swimming in Different Wetsuits and Across Different Paces.

A triathlon wetsuit is an important piece of equipment during the swim portion of the triathlon for the benefits of thermoregulation and additional buoyancy. However, a lack of knowledge exists about whether or not shoulder muscle activity is influenced by wearing a wetsuit. The purpose of this study was to determine if there were changes in shoulder muscle activity during front crawl with four different wetsuit conditions: Full sleeve (FSW), Sleeveless (SLW), Buoyancy shorts (BS), No wetsuit (NWS) in three different subjective swimming paces (slow, medium, and fast). Eight subjects (5 males, 3 females: mean ± SD, age = 39.1 ± 12.5 years; height = 1.8 ± 0.1 m; mass = 74.6 ± 12.9 kg; percent body fat = 19.0 ± 7.8%) completed twelve total swim conditions (4 wetsuits x 3 swimming pace) in a 25-m indoor pool. Muscle activity in anterior deltoid (AD) and posterior deltoid (PD) were measured using a wireless waterproofed electromyography (EMG) system. Stroke rate (SR) was calculated using the time to complete five-stroke cycles. The AD, PD EMG, and SR were compared using ANOVA with repeated measures. None of the dependent variables showed the interaction between wetsuit conditions and swimming paces (p > 0.05). Both AD and PD muscle activity as well as SR were influenced by swimming pace (p < 0.05) but not wetsuit conditions (p > 0.05). In conclusion, shoulder muscle activity and SR were not influenced by types of wetsuits but influenced by swimming pace.

Myosin5a tail associates directly with Rab3A-containing compartments in neurons.

Myosin-Va (Myo5a) is a motor protein associated with synaptic vesicles (SVs) but the mechanism by which it interacts has not yet been identified. A potential class of binding partners are Rab GTPases and Rab3A is known to associate with SVs and is involved in SV trafficking. We performed experiments to determine whether Rab3A interacts with Myo5a and whether it is required for transport of neuronal vesicles. In vitro motility assays performed with axoplasm from the squid giant axon showed a requirement for a Rab GTPase in Myo5a-dependent vesicle transport. Furthermore, mouse recombinant Myo5a tail revealed that it associated with Rab3A in rat brain synaptosomal preparations in vitro and the association was confirmed by immunofluorescence imaging of primary neurons isolated from the frontal cortex of mouse brains. Synaptosomal Rab3A was retained on recombinant GST-tagged Myo5a tail affinity columns in a GTP-dependent manner. Finally, the direct interaction of Myo5a and Rab3A was determined by sedimentation velocity analytical ultracentrifugation using recombinant mouse Myo5a tail and human Rab3A. When both proteins were incubated in the presence of 1 mm GTPγS, Myo5a tail and Rab3A formed a complex and a direct interaction was observed. Further analysis revealed that GTP-bound Rab3A interacts with both the monomeric and dimeric species of the Myo5a tail. However, the interaction between Myo5a tail and nucleotide-free Rab3A did not occur. Thus, our results show that Myo5a and Rab3A are direct binding partners and interact on SVs and that the Myo5a/Rab3A complex is involved in transport of neuronal vesicles.

Rocker-bottom, profile-type shoes do not increase lower extremity muscle activity or energy cost of walking.

The purpose of this study was to determine if wearing rocker-bottom shoes with compliant midsoles (RB) influences muscle activity and metabolic cost of walking. Furthermore, we sought to determine if weight differences between shod conditions accounted for any potential change. Twenty-eight subjects (17 women, 11 men, age 22.8 ± 6.6 years; weight 72 ± 20 kg; height 170 ± 6.7 cm; percent body fat 23.0 ± 11.7) walked on a treadmill (0% grade) for 10 minutes at a self-selected speed plus 10% (1.3 ± 0.2 m·s) in each of the following laboratory-provided shoes: flat-bottomed shoe (W), flat-bottomed shoe weight-matched to RB (WM), and RB. Muscle activity of the right side biceps femoris (BF), rectus femoris (RF), gastrocnemius (GA), and tibalis anterior (TA) was recorded for 30 seconds at the beginning, middle, and ending of the 10-minute walk using an electromyography (EMG) system. The average (AVG) and root mean square (RMS) were calculated from full-wave rectified EMG data at each interval. The rate of oxygen consumption (V[Combining Dot Above]O2) was measured for 10 minutes during each condition. A 3 (shoe) × 3 (time) repeated-measures analysis of variance (ANOVA) was used to compare each EMG-dependent variable (AVG and RMS EMG of each muscle), and repeated measures ANOVA was used to test V[Combining Dot Above]O2. Muscle activity (for any muscle) was not influenced by the interaction of shoe and time (p > 0.05). The AVG and RMS for RF, BF, and GA, including V[Combining Dot Above]O2, were not different among shod conditions (W: 9.7 ± 0.6 ml·kg·min; WM: 10.0 ± 0.5 ml·kg·min; RB: 10.1 ± 0.5 ml·kg·min), whereas TA AVG and RMS were lower during RB (p < 0.05). It seems that there is no increase in muscle activity or metabolic cost while wearing RB beyond the flat-bottomed shoe despite there being the rocker-profile design and mass differences.