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.

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.

A Study Comparing Gait and Lower Limb Muscle Activity During Aquatic Treadmill Running with Different Water Depth and Land Treadmill Running.

Aquatic treadmill running is a partial weight-bearing exercise for rehabilitation. The purpose of this study was to investigate the surface electromyography activities of the rectus femoris, tibialis anterior, biceps femoris and medial head of gastrocnemius, and gait kinematics during aquatic treadmill running in water levels at waist, mid-thigh and mid-shin and on land. Seventeen healthy subjects (9 males and 8 females) were recruited by convenience sampling. Participants performed 2-min aquatic treadmill running at a specific speed for each water depth. The test speed was selected based upon the speed that elicited 110 steps per min. The surface electromyography data of lower limb muscles and the joint angles at three different water depths and on land were collected to evaluate the muscle activity and gait kinematics using a waterproofed surface electromyography system and inertial measurement unit for each muscle. Results showed that rectus femoris electromyography was different between depths during the swing and stance phases. Likewise, biceps femoris and tibialis anterior electromyography were different between depths for the swing phase. However, it was not the case for gastrocnemius electromyography. Peak flexion angles in both left and right hips were different between depths. A significant increase in a stance/swing ratio was observed with rising water depths. Water depth influenced muscle activity as well as kinematics. Aquatic treadmill running in the mid-thigh level should be further evaluated for its effectiveness, training value and applicability.

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.

Calcium triggers the dissociation of myosin-Va from ribosomes in ribonucleoprotein complexes.

The sorting of RNAs to specific regions of the cell for local translation represents an important mechanism directing protein distribution and cell compartmentalization. While significant progress has been made in understanding the mechanisms underlying the transport and localization of mRNAs, the mechanisms governing ribosome mobilization are less well understood. Ribosomes present in the cytoplasm of multiple cell types can form ribonucleoprotein complexes that also contain myosin-Va (Myo5a), a processive, actin-dependent molecular motor. Here, we report that Myo5a can be disassociated from ribosomes when ribonucleoprotein complexes are exposed to calcium, both in vitro and in vivo. We suggest that Myo5a may act as a molecular switch able to anchor or release ribosomes from the actin cytoskeleton in response to intracellular signaling.

Running status and history: A self-report study.

OBJECTIVES: The purpose of the current study was to compare injury and running history among current and former runners who consider themselves either injured or uninjured. DESIGN: Cross-sectional survey. SETTING: Online survey, available to any individuals over the age of 18 who currently run (runners) or who once ran regularly but are no longer running (former runners). PARTICIPANTS: 312 participants (age 38 ±â€¯12 years, 219 males, 89 females, 4 did not disclose) completed the survey. MAIN OUTCOME MEASURES: This study assessed injury incidence, consequences of injury such as time off, and reported injury diagnoses and treatments. Chi-square and frequency analyses were calculated to describe running status, injury counts, and response to injury. RESULTS: Most participants (80%) reported 1 + running injury. 775 total injuries were reported. The four most common injuries were iliotibial band syndrome (34%), plantar fasciitis (30%), strained thigh/hip muscle (25%), and medial tibial stress syndrome (22%). About 40% of participants continued to run with these injuries. CONCLUSIONS: Injury frequencies (80%) agreed with those reported in the literature. The results of this study also support the notion that running injuries exist on a continuum of severity and that the individual response to injury is complex and determined by various factors.

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.

Running Economy While Running in Shoes Categorized as Maximal Cushioning.

The purpose of the study was to determine if running economy was influenced by wearing maximal cushioning shoes vs. control (neutral cushioning) shoes. Participants (n=10, age=28.2±6.1yrs; mass=68.1±10.2 kg; height=170±6.1 cm) completed two experiments. Each experiment included running conditions wearing control and maximal cushioning shoes. In Experiment 1, participants ran on a treadmill at three speeds in each shoe condition (6 total conditions). The speeds were: 1) preferred speed, 2) preferred speed + 0.447 m·s-1, and 3) preferred speed - 0.447 m·s-1. In Experiment 2, participants ran on a treadmill at two inclines (0%, 6%) in each shoe condition (4 total conditions) at preferred speed. Experiments were conducted on separate days with Experiment 1 first. For all conditions, participants ran for 8-10 minutes while rate of oxygen consumption (VO2) was recorded. Average VO2 during steady state for each running condition was calculated. For Experiment 1, a 2 (shoe) × 3 (speed) repeated measures ANOVA (α=0.05) was used. For Experiment 2, a 2 (shoe) × 2 (incline) repeated measures ANOVA (α=0.05) was used. Rate of oxygen consumption was not influenced by the interaction of speed and shoe (p=0.108); VO2 was different between speeds (p<0.001), but not between shoes (p=0.071). Rate of oxygen consumption was not influenced by the interaction of incline and shoe (p=0.191); VO2 was greater for incline vs. level (p<0.001), but not different between shoes (p=0.095). It is concluded that a maximal cushioning running shoe did not influence running economy when compared to a control shoe (neutral cushioning running shoe).

Effects of treadmill running velocity on lower extremity coordination variability in healthy runners.

With a growing interest in coordination variability and its role in endurance running, it is important to identify the effect of running velocity. The purpose of the current study was to investigate the effect of treadmill running velocity on the coordination and variability of coordination of lower extremity couplings of healthy runners during stance. Fourteen apparently healthy runners ran on a split-belt force instrumented treadmill at five different velocities. Continuous relative phase (CRP) was used to quantify coordination and variability (vCRP) between lower extremity couplings of the right limb (thigh-shank, thigh-foot, shank-foot) during three phases of stance (loading, mid stance, and propulsion). Multiple one-way repeated measure ANOVAs were conducted to identify differences among velocity conditions at each phase and discrete events (initial foot contact, peak knee flexion during stance, and toe-off). Thigh internal/external rotation (IR/ER)-Shank abduction/adduction (AB/AD) coupling was different during the propulsive phase (p = 0.02). Thigh flexion/extension-Shank flexion/extension showed the greatest differences in vCRP across velocity conditions with differences occurring during loading phase, mid stance, propulsive phase, and peak flexion (p < 0.05). Additionally, significant differences were seen in Thigh FL/EX-Shank FL/EX (toe-off, p = 0.01) and Thigh FL/EX-Foot inversion/eversion (IN/EV) (toe-off, p = 0.032). Interestingly, the decreases in vCRP values were accompanied by changes in center of mass vertical motion during stance, but not knee flexion angles. Increases in running velocity led to a more constrained running pattern through a reduction in degrees of freedom.

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.

Influence of stride frequency manipulation on muscle activity during running with body weight support.

BACKGROUND: Running with body weight support (BWS) has been used for physical fitness enhancement. Nevertheless, gait mechanics of running with BWS is not fully understood. RESEARCH QUESTION: We investigated influence of stride frequency manipulation on muscle activity during running at various BWS conditions. METHODS: Nineteen participants (23.8 ±â€¯4.1 years) ran on a lower body positive pressure treadmill at their preferred speed and preferred stride frequency (PSF) for 0%BWS, 50%BWS, and 80%BWS conditions. Preferred speed and PSF were selected for each of the BWS conditions. The stride frequency conditions consisted of running at PSF, PSF+10%, and PSF-10%. Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GA) were measured. RESULTS: RF and BF during running at the PSF+10% were higher than when running at the PSF, regardless of BWS (P < 0.01). Additionally, RF and TA during running at the PSF-10% were higher than when running at the PSF, regardless of BWS (P < 0.05). Furthermore, RF, TA, GA, and PSF during running decreased with increasing BWS (P < 0.05), although preferred speed increased with increasing BWS (P < 0.001). SIGNIFICANCE: These observations suggest that manipulating stride frequency by 10% from the PSF during running produces greater RF, BF, and TA than when running at the PSF, regardless of BWS. Furthermore, it was suggested that a change in BWS influences RF, TA, GA, PSF, and preferred speed during running. Such information may be useful to enable the practitioner to refine the use of running with BWS in exercise programs.

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.

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.

Comparison of pre-contact joint kinematics and vertical impulse between vertical jump landings and step-off landings from equal heights.

Although impact phase differences between vertical jump landings (VJL) and step-off landings (STL) may be related to task-specific pre-contact strategies, pre-contact mechanics are rarely examined. Thus, pre-contact kinematics and vertical ground reaction force (vGRF) impulse were examined between VJL and STL. Ten health adults (20.9 ±â€¯1.6 yrs; 167.8 ±â€¯4.2 cm; 68.5 ±â€¯7.15 kg) performed 15 VJL and 15 STL from equal heights. Limb (lead; trail) by task (VJL; STL) ANOVAs (α = 0.05) compared hip, knee, and ankle joint angles 150 ms pre-contact, 100 ms pre-contact, 50 ms pre-contact, and at ground contact. Joint angular displacement was also evaluated between 150 ms pre-contact and ground contact. vGRF impulse was compared during the loading (ground contact to peak vGRF) and attenuation (peak vGRF to end of impact) phases. Greater hip flexion angles occurred during STL versus VJL at each event except 150 ms pre-contact (p ≤ .004). Trail limb knee flexion angles were greater at each event when compared to the lead limb during STL (p ≤ .019). Greater trail limb knee flexion angles occurred during STL versus VJL at all four events (p ≤ .018), while greater plantarflexion angles occurred at all four events during VJL versus STL (p ≤ .034). During STL, greater trail limb plantarflexion angles were detected at each event versus the lead limb (p < .001). Lesser hip, lead and trail limb knee displacement occurred during STL versus VJL (p < .05). Greater vGRF impulse was detected during the loading phase of VJL (<.001), while greater vGRF impulse occurred during the attenuation phase of STL (p = .025). These tasks are characterized by distinct pre-contact kinematic strategies and post-contact kinetics. The task utilized in practice should reflect the requirements of the population of interest.

Is the Relationship Between Stride Length, Frequency, and Velocity Influenced by Running on a Treadmill or Overground?

The purpose of the study was to compare the relationship between stride length (SL), stride frequency (SF), and velocity while running on a treadmill and overground. Participants (n=10; 22.3±2.6 yrs; 1.71±.08 m; 71.4±15.5 kg) completed a total of 14 runs (7 treadmill, 7 overground) with each run at a different velocity. SL, SF, and velocity data were recorded using wearable technology (Garmin, Fenix2). The outdoor trials occurred first. The treadmill velocities were selected to match the range of velocities used overgroud. SL vs. velocity plots were generated for treadmill and overground data for each participant and fit with a 2nd order polynomial in the form of SL=Av2+Bv+C. Each equation coefficient (i.e., A, B, C) was averaged across participants and compared between treadmill and overground using paired t-tests. The A coefficient (v2 term) was different treadmill vs. overground (p=0.031). Neither B (p=0.136) nor C (p=0.260) coefficients were different treadmill vs. overground. It was concluded that the A coefficient (v2 term) for SL vs. velocity was larger during overground vs. treadmill running. This is an indication that the strategy of changing SL across velocities was different when on the treadmill vs. overground. Specifically, while running on a treadmill, SL continued to increase in a more linear manner than when running overground.

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.

Muscle activity during backward and forward running with body weight support.

We investigated muscle activity during backward (BR) and forward (FR) running with body weight support (BWS). Ten participants completed BR and FR on a lower body positive pressure treadmill while selecting a preferred speed (PS) for different BWS conditions (0%, 20%, 40%, 60%, and 80%BWS). Muscle activity from the rectus femoris (RF), biceps femoris (BF), tibialis anterior (TA), and gastrocnemius (GA), rating of perceived exertion (RPE), preferred stride frequency (PSF), and PS were measured. Magnitude of muscle activity (BF, TA, and GA), RPE, PSF, and PS were not influenced by the interaction of direction and BWS (P>0.05). BF, TA, and GA were not different between directions (P>0.05) but were different between BWS conditions (P<0.01). RF was influenced by the interaction of direction and BWS (P<0.01). RF, BF, TA, and GA during BR were lower with increasing BWS. RF during BR was 59-86% higher than that of FR within BWS condition. RPE was lower with increasing BWS (P<0.001), regardless of direction of locomotion. PSF was lower and PS was higher during BR and FR with increasing BWS (both P<0.001). PSF during BR was 6-9% higher than that of FR. PS during BR was 24-31% lower than that of FR. These observations demonstrate that a change in BWS influences magnitude of muscle activity, PS, PSF, and RPE for both BR and FR. However, a change in direction of locomotion may not influence magnitude of muscle activity or RPE during running for a given BWS, even though muscle activity pattern, PS, and PSF were different between BR and FR.

Three-dimensional impact kinetics with foot-strike manipulations during running.

BACKGROUND: Lack of an observable vertical impact peak in fore/mid-foot running has been suggested as a means of reducing lower extremity impact forces, although it is unclear if impact characteristics exist in other axes. The purpose of the investigation was to compare three-dimensional (3D) impact kinetics among foot-strike conditions in over-ground running using instantaneous loading rate-time profiles. METHODS: Impact characteristics were assessed by identifying peak loading rates in each direction (medial-lateral (ML), anterior-posterior (AP), vertical, and 3D resultant) following foot-strike instructions (fore-foot, mid-foot, subtle heel, and obvious heel strike). Kinematic and kinetic data were analyzed among 9 male participants in each foot-strike condition. RESULTS: Loading rate peaks were observed in each direction and foot-strike condition, differing in magnitude by direction (3D resultant and vertical > AP > ML, p ≤ 0.031) and foot-strike: ML (fore-foot and mid-foot strike > obvious heel strike, p ≤ 0.032), AP (fore-foot and mid-foot strikes > subtle-heel and obvious heel strikes, p ≤ 0.023). In each direction, the first loading rate peak occurred later during heel strike running relative to fore-foot (p ≤ 0.019), with vertical and 3D resultant impact durations exceeding shear (ML and AP, p ≤ 0.007) in each condition. CONCLUSION: Loading rate-time assessment identified contrasting impact characteristics in each direction and the 3D resultant following foot-strike manipulations, with potential implications for lower extremity structures in running.

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.