Point/Counterpoint: Are Specific Spine Stabilization Exercises Necessary for Athletes?

The issue of spine stabilization has received considerable attention in recent years; although there are many proponents for specific training of spinal musculature, there is debate as to whether it is beneficial and required for athletes

Compensatory changes in female running mechanics during a simulated 10 km race

During a 10 km run at race pace, changes in lower extremity mechanics have been reported in male runners however mechanical changes over 10 km in female runners is unknown. Thus we aimed to examine running mechanics in females during a simulated 10 km race on a treadmill. Nine female distance runners (age: 32.1±4.2 yrs; ht: 166.7 ± 7.4 cm; wt: 57.8 ± 7.0 kg; VO2max = 3.24 ± 0.50 L/min) completed graded exercise testing (Day 1); 10km time trial (Day 2); and simulated 10km treadmill run (DAY 3; 95 % of running velocity from Day 2 time-trial). Mechanical data sampled at 120Hz using a 6-camera optoelectronic motion capture system and effort (Rating of Perceived Exertion - RPE) were measured at 50, 1450, 2950, 4450, 5950, 7450, 8950 and 9950 metres. Maximum voluntary contraction of knee extensors was measured pre-post. Seven participants decreased MVC (1-21% decrease) and RPE increased from 12 (50m) to 19 (9950m). Step frequency decreased 3 steps/min (p<0.05) and step length increased 3cm. Max knee extension and max knee flexion increased from 50m to 9950m and hip height was lowered over the 10km time-trial. These results indicate that whole body fatigue influences RPE and is associated with mechanical changes to maintain pace in female runners. Specifically, the combination of knee extension and knee flexion increases likely reduces limb inertia as the runner fatigues minimizing decreases in step frequency and improving step length. These results are the first to illuminate the fatigue related intrinsic coping mechanisms of female runners at race pace

Distribution of lower extremity work during clean variations performed with different effort

The purpose of this research was to investigate how lower extremity work was distributed during the pull of cleans performed lifting the barbell to the minimum height required to receive it in a full squat (minimal height clean); or with maximum effort to elevate the barbell as high as possible and receiving it in either a full (maximal effort clean) or partial (power clean) squat. Eight weightlifters screened for proficient technique performed these clean variations at 80% of one repetition maximum. Work performed on the barbell and by the lower extremity net joint moments (NJM) was computed from marker trajectories and ground reaction forces. Total barbell work, lower extremity NJM work, knee extensor work, and knee joint excursion during the second pull was lower in the minimal height clean than the maximal effort and power cleans (P < 0.05). This research demonstrates that more knee extensor work is performed in the second pull of maximal effort and power cleans compared to the minimal height clean. The larger knee extensor work performed is due to larger knee joint excursion during the second pull of the maximal effort and power cleans, but not larger knee extensor NJM

Myosin heavy chain isoform expression: Influence on isoinertial and isometric performance

Thirty-six healthy men with varying degrees of physical training background performed maximal-effort isometric and isoinertial knee extensor actions, with relative loads equal to 40% and 70% of one-repetition maximum. Force, velocity, and power were derived from force and linear position transducers at 500 Hz. Biopsies were taken from the vastus lateralis and analyzed by SDS-PAGE for relative myosin heavy chain (MHC) content. Relative MHC IIx content was included in a regression model, and explained variance noted. Relative MHCI content was subsequently added to the regression model to determine what, if any, additional variance was explained beyond that of MHC IIx. Results indicated that no relationship (r = 0.0 to 0.1) exists between the relative expression of MHC isoforms from the vastus lateralis and isometric/isoinertial performance in a population with diverse training backgrounds. Lack of nervous system adaptations in the untrained subjects in the study possibly attenuates the significant relationship between MHC and in-vivo muscle performance previously established in trained populations. Copyright © Taylor & Francis LLC

β2-Adrenergic receptor downregulation and performance decrements during high-intensity resistance exercise overtraining

Previous research on overtraining due to excessive use of maximal resistance exercise loads [100% 1 repetition maximum (1 RM)] indicates that peripheral muscle maladaptation contributes to overtraining-induced performance decrements. This study examined the cellular and molecular responses of skeletal muscle to performance decrements due to high-relative-intensity (%1 RM) resistance exercise overtraining. Weight-trained men were divided into overtrained (OT, n = 8) and control (Con, n = 8) groups. The OT group performed 10 X 1 at 100% 1 RM daily for 2 wk, whereas the Con group performed normal training 2 days/wk. Muscle biopsies from the vastus lateralis muscle, voluntary static and dynamic muscle performances, and nocturnal urinary epinephrine were assessed before (pre) and after (post) overtraining. Overtraining occurred as indicated by a decrease in 1-RM strength for the OT group (mean ± SE; OT pre = 159.3 ± 10.1 kg, OT post = 151.4 ± 9.9 kg, Con pre = 146.0 ± 12.9 kg, Con post = 144.9 ± 13.3 kg), as well as a 36.3% decrease in mean power at 100% 1-RM loads. Normal training could be resumed only after 2-8 wk of training cessation. Muscle β2-adrenergic receptor (β2-AR; fmol/mg protein) density significantly decreased by 37.0% for the OT group and was unchanged for the Con group (-1.8%). Nocturnal urinary epinephrine for the OT group increased by 49%, although this was not significant (effect size = 0.42). The ratio of nocturnal urinary epinephrine to β2-AR density suggested a decreased β2-AR sensitivity for the OT group (2.4-fold increase). Overtraining occurred based on decreased muscular force and power. Desensitization of the β2-AR system suggests that this may be an important contributor to performance decrements due to excessive use of maximal resistance exercise loads. Copyright © 2006 the American Physiological Society

Myosin heavy chain isoform expression and in vivo isometric performance: a regression model

This investigation estimated the amount of variance in voluntary in vivo muscle performance that can be explained by relative myosin heavy chain (MHC) isoform expression. The role of the relative expression of these proteins in relation to in vitro force and velocity performance is well understood, but the in vivo model is less clear. Twenty-two men and women (mean ± SD age, 27 ± 6 years) performed isometric knee extensor actions in which peak force and rate of force development (RFD) were measured. The results of regression analysis showed that the inclusion of MHC IIb explained a significant (19.9%, p \u3c 0.05) amount of variance in relative peak force (adjusted for muscle mass) and 14.1% of the variance in the first half of the rise phase of the force-time curve (RFD0-50%) (p \u3c 0.1). The addition of MHC I into this model explained a significant (p \u3c 0.05) amount of variance above that accounted for by MHC IIb in RFD (45.4%), RFD0-50%, (50.8%), and RFD 50-100% (second half of the rise phase of the force-time curve) (37.4%). Since the percentage of MHC IIb is reduced rather quickly with training, these data suggest that peak force may also be affected quickly by training. The percentage of MHC I has a longer course for change with training; therefore, it may be inferred that the greatest changes in RFD variables will likely occur during a longer course. © 2005 National Strength & Conditioning Association

Consistency of lower-body dimensions using surface landmarks and simple measurement tools

Caia, J, Weiss, LW, Chiu, LZF, Schilling, BK, and Paquette, MR. Consistency of lower-body dimensions using surface landmarks and simple measurement tools. J Strength Cond Res 30(9): 2600-2608, 2016 - Body dimensions may influence various types of physical performance. This study was designed to establish the reliability and precision of bilateral lower-body dimensions using surface anatomic landmarks and either sliding calipers or goniometry. Fifty university students (25 men and 25 women) were measured on 2 separate occasions separated by 48 or 72 hours. A small digital caliper was used to acquire longitudinal dimensions of the feet, whereas a larger broad-blade caliper was used to measure lower-limb, hip, and pelvic dimensions. Quadriceps angle (Q-angle) was determined through surface goniometry. Data for all foot and lower-limb dimensions were both reliable and precise (intraclass correlation coefficient (ICC) ≥0.72, SEM 0.1-0.5 cm). Measures of Q-angle were also reliable and precise (ICC ≥0.85, SEM 0.2-0.4°). Findings from this investigation demonstrate that lower-body dimensions may be reliably and precisely measured through simple practical tests, when surface anatomic landmarks and standardized procedures are used. Although intertester reliability remains to be established, meticulous adherence to specific measurement protocols is likely to yield viable output for lower-body dimensions when more sophisticated methods are unavailable or inappropriate

Reach height and jump displacement: Implications for standardization of reach determination

Vertical jump performance is often assessed using jump-and-reach tests. The exact procedure used for determining standing reach height and jump height has a large effect on the resultant displacement. The purpose of this investigation was to determine the influence of 4 methods of standing reach height measurement and Vertec™ jump height measurement against 2 force plate methods of jump displacement determination (impulse and flight-time methods). Fifteen men with various training backgrounds performed 2 each of countermovement, restricted (no arm swing) and static start vertical jumps. Reach height was determined using 4 methods; either a 1-or overlapped 2-hand reach, flat footed or with plantar flexion. All jumps were performed on a force platform. The best jump of each type based on Vertec™ displacement was used for analysis. Repeated-measures of analysis of variance for each jump type was used for analysis with Bonferroni post hoc for pairwise comparisons of jump measurement style. All jump displacements for similar types were significantly intercorrelated with a minimum r-value of 0.84. Impulse vs. flight time was the only pairwise comparison of measurement type for which similar values were noted. The onehand reach with plantar flexion was the method of reach that was closest to the impulse and flight-time methods, and thus should be the preferred choice when using jump-and-reach tests to determine jump displacement. In all cases, the Vertec™ overestimates the displacement of the COM based on force plate methods. When comparing groups of individuals from different data sets, one must consider both the method of reach height (if performed) and jump displacement to make valid comparisons. If plantar flexion with a 1-hand reach is not used during reach measurement, jump displacement will be erroneously high. © 2010 National Strength and Conditioning Association