Background: One of the possible mechanisms leading to shoulder injury may be a strength imbalance between those muscles that accelerate
the upper limb and those responsible for deceleration. Many ...studies have examined shoulder balance through a concentric strength
ratio of external and internal shoulder rotator muscles.
Hypothesis: A functional external eccentric-to-internal concentric ratio may be a better identifier of muscular imbalance in dominant
and nondominant shoulders of throwers and nonthrowers.
Study Design: Controlled laboratory study.
Methods: Eccentric external and concentric internal peak torques were measured bilaterally in 59 men (16 throwers and 43 nonthrowers)
at 300 deg/sec. Subjects were tested in the supine position with the shoulder abducted to 90° and the elbow flexed to 90°.
Results: Throwers exhibited significantly lower ratios than nonthrowers in their dominant limb; there was no difference between groups
for the nondominant limb.
Conclusions: The lower ratio in the throwersâ dominant limb was attributed to significantly greater concentric internal rotation torques
without concomitant eccentric external torque gains.
Clinical Relevance: Rehabilitation and injury prevention regimens that include functional exercises to improve eccentric external rotation strength
may bring more balance to the dominant shoulder of throwing athletes.
If the efficiency of human movement patterns could be improved using exercise, this could lead to more effective musculoskeletal disease-injury prevention and rehabilitation programs. It has been ...suggested that an efficient squat movement pattern emphasizes the use of the large hip extensors instead of the smaller knee extensors. The purpose of this study was to determine whether a counterbalanced squat (CBS) could produce a more hip-dominant and less knee-dominant squat movement pattern as compared with a regular squat (RS). There were 31 recreationally trained college-aged participants (15 male, 16 female) who performed 10 squats (5 CBS and 5 RS), while segment kinematics, ground reaction forces, and muscle (gluteus maximus GM, quadriceps, hamstrings) electromyographic (EMG) activations were recorded. Peak sagittal plane net joint moments and joint ranges of motion at the hip, knee, and ankle joints along with peak and integrated EMG activation levels for all 3 muscles were compared using analysis of variance (squat type × sex). The results revealed that the CBS increased the hip joint moment and GM activation, while it decreased the knee joint moment and quadriceps activation as compared with the RS. Therefore, the CBS produces a more hip-dominant and less knee-dominant squat movement pattern and could be used in exercise programs aimed at producing more hip-dominant movement patterns.
•Running injury etiology is multifactorial and prospective analysis is encouraged.•Kinematics and kinetics were compared between injured and uninjured runners.•External knee adduction moments were ...greater in injured runners.•Peak ankle eversion velocity was greater in injured runners.•These variables may be potential risk factors for injury in runners.
Collegiate cross country runners are at risk for running related injuries (RRI) due to high training volume and the potential for aberrant lower extremity biomechanics. However, there is a need for prospective research to determine biomechanical risk factors for RRI. The purpose of this study was to prospectively compare ankle, knee, and hip kinematics and kinetics and ground reaction force characteristics between injured and non-injured cross country runners over a 14-week season. Biomechanical running analyses were conducted on 31 collegiate-cross country runners using a 3-dimensional motion capture system and force plate prior to the start of the season. Twelve runners were injured and 19 remained healthy during the course of the season. Peak external knee adduction moment (KAM), a surrogate for frontal plane knee loading, and peak ankle eversion velocity were greater in runners who sustained an injury compared to those who did not, and no differences were noted in ground reaction force characteristics, or hip kinematics and kinetics. Reducing the KAM and ankle eversion velocity may be an important aspect of preventing RRI.
The purpose of this study was to determine the effect of foot strike patterns and converted foot strike patterns on lower limb kinematics and kinetics at the hip, knee, and ankle during a shod ...condition. Subjects were videotaped with a high speed camera while running a 5km at self-selected pace on a treadmill to determine natural foot strike pattern on day one. Preferred forefoot group (PFFG, n = 10) and preferred rear foot group (PRFG, n = 11) subjects were identified through slow motion video playback (n = 21, age = 22.8±2.2 years, mass = 73.1±14.5 kg, height 1.75 ± 0.10 m). On day two, subjects performed five overground run trials in both their natural and unnatural strike patterns while motion and force data were collected. Data were collected over two days so that foot strike videos could be analyzed for group placement purposes. Several 2 (Foot Strike Pattern -forefoot strike FFS, rearfoot strike RFS) x 2 (Group - PFFG, PRFG) mixed model ANOVAs (p < 0.05) were run on speed, active peak vertical ground reaction force (VGRF), peak early stance and mid stance sagittal ankle moments, sagittal plane hip and knee moments, ankle dorsiflexion ROM, and sagittal plane hip and knee ROM. There were no significant interactions or between group differences for any of the measured variables. Within subject effects demonstrated that the RFS condition had significantly lower (VGRF) (RFS = 2.58 ± .21 BW, FFS = 2.71 ± 0.23 BW), dorsiflexion moment (RFS = -2.6 1± 0.61 Nm·kg(-1), FFS = -3.09 ± 0.32 Nm·kg(-1)), and dorsiflexion range of motion (RFS = 17.63 ± 3.76°, FFS = 22.10 ± 5.08°). There was also a significantly higher peak plantarflexion moment (RFS = 0.23 ± 0.11 Nm·kg(-1), FFS = 0.01 ± 0.01 Nm·kg(-1)), peak knee moment (RFS = 2.61 ± 0.54 Nm·kg(-1), FFS = 2.39 ± 0.61 Nm·kg(-1)), knee ROM (RFS = 31.72 ± 2.79°, FFS = 29.58 ± 2.97°), and hip ROM (RFS = 42.72 ± 4.03°, FFS = 41.38 ± 3.32°) as compared with the FFS condition. This research suggests that acute changes in foot strike patterns during shod running can create alterations in certain lower limb kinematic and kinetic measures that are not dependent on the preferred foot strike pattern of the individual. This research also challenges the contention that the impact transient spike in the vertical ground reaction force curve is only present during a rear foot strike type of running gait. Key pointsFootstrike pattern changes should be individually considered and implemented based on individual histories/abilitiesForefoot strike patterns increase external dorsiflexion momentsRearfoot strike patterns increase external knee flexion momentsRecreational shod runners are able to mimic habitual mechanics of different foot strike patterns.
Considering the importance of the vertical jump in several sports, an optimal warm-up protocol may help athletes perform at their maximum level. The purpose of this study was to investigate the ...potentiating effects of different levels of external resistance (weighted vest) during box jumps on vertical jump performance. Twenty resistance trained men (age 22.45 +/- 1.73 years, height 176.83 +/- 6.67 cm, mass 76.98 +/- 8.56 kg) participated in this study. Subjects performed 5 jumps onto a box equivalent in height to their lateral femoral condyle. After a 2-minute rest period, subjects performed 3 vertical jumps with the greatest height being recorded. On day 1, each subject performed a control condition with no external resistance to establish a baseline vertical jump height. On the following days, they performed 4 random jump conditions with a weight vest equivalent to 5, 10, 15, or 20% of their body weight then rested for 2 minutes before performing 3 posttest vertical jumps. Results demonstrated no significant interaction of condition by time for vertical jump height. However, there was a significant main effect for time (p < 0.05) with posttest jump height (22.99 +/- 3.35 in.) being greater than pretest jump height (22.69 +/- 3.37 in.). Performing an active dynamic warm-up with or without a weighted vest produced significantly greater posttest vertical jump performance. A dynamic warm-up may improve vertical jump performance, albeit to a very small increment.
High-force activities have demonstrated postactivation potentiation (PAP) and may enhance performance in athletes; however, the efficacy of high-force activities to generate PAP in recreationally ...trained men remains unclear. The purpose of this study was to investigate the effect of high-force back squat volume on vertical jump (VJ) height, ground reaction force (GRF), impulse (IMP), and takeoff velocity (TOV) in recreationally trained men. Sixteen recreationally trained men (age 24.56 +/- 2.10 years, height 174.53 +/- 8.54 cm, mass 84.59 +/- 14.75 kg, and 1 repetition maximum 1RM back squat 124.71 +/- 17.58 kg) with at least 1 year of back squat experience completed 5 testing sessions separated by a minimum of 72 hours' rest. On session 1, subjects completed VJ testing without a potentiating exercise intervention (control condition) in a test-retest fashion (3 VJs, 5 minutes seated rest, and 3 more VJs) and performed 1RM back squat testing. Subjects completed the subsequent 4 testing sessions in a test-retest fashion (3 VJs, experimental condition, 5 minutes seated rest, and 3 more VJs) in random order. The 4 experimental conditions required subjects to perform the back squat using a load of 85% 1RM with volumes of 1 x 2, 1 x 3, 1 x 4, or 1 x 5. Analysis of variance revealed no significant (p > 0.05) condition by time interactions for any dependent variable; however, there were significant (p < 0.05) main effects for time for GRF (pre 2,123.74 +/- 422.86 N, > post 2,094.53 +/- 390.99 N) and IMP (pre 210.88 +/- 100.97 Nxs, > post 204.63 +/- 106.14 Nxs) but not for VJ or TOV. These results suggest that 85% 1RM back squat volume assignments do not produce a VJ potentiation response in recreationally trained men.
Previous research has investigated the force-time curve characteristics of isometric and dynamic muscle actions; however, few studies have addressed their relationship to dynamic exercise ...velocity-time variables. The purpose of this study was to investigate relationships between velocity-time characteristics (high pull and vertical jump peak velocity and rate of velocity development HPPV, HPRVD, VJPV, VJRVD), force-time characteristics (isometric peak force IsoPF, body mass adjusted isometric peak force IsoPF/BM, isometric rate of force development at different millisecond windows IsoRFD50-250, dynamic peak force HPPF, body mass adjusted dynamic peak force HPPF/BM), and vertical jump height (VJHeight). Nineteen recreationally trained men (age 23.89 ± 2.92 yr; height 176.32 ± 7.06 cm; mass 78.76 ± 16.50 kg) completed 2 testing sessions. The first session consisted of 3 isometric mid-thigh pulls on a force plate with each repetition held for 3 seconds. On the second testing session, subjects completed 3 dynamic mid-thigh high pulls with 30% IsoPF followed by 3 vertical jumps on a force plate. The HPRVD correlated with IsoRFD50 (r = 0.52) and IsoRFD100 (r = 0.49). The HPPV correlated with IsoPF/BM (r = -0.60), IsoRFD50 (r = 0.56), and IsoRFD100 (r = 0.56). The VJHeight correlated with IsoPF/BM (r = 0.61), whereas VJPV correlated with IsoPF/BM (r = 0.62). These correlations suggest that explosive isometric force production within 50 to 100 milliseconds may influence the ability to accelerate an implement or body and attain high velocity, albeit in a moderate fashion. In addition, body mass adjusted strength may positively influence vertical jump parameters.
Golf has the potential to keep people active well into their later years. Injuries to the target side knee have been reported in golfers, yet no mechanisms for these injuries have been proposed. The ...loads on the knee during the golf swing may be insufficient to cause acute injury, yet they may be a factor in the progression of overuse/degenerative conditions; therefore, research developing swing modifications that may alter loading of the knee is warranted. It has been suggested that the proper golf set-up position has the target-side foot externally rotated but no reasoning for this modification has been provided. Frontal plane knee moments have been implicated in many knee pathologies. Therefore, this study used a 3-dimensional link segment model to quantify the frontal plane knee moments during the golf swing in a straight (STR) and externally rotated (EXT) target-side foot position. Subjects were 7 collegiate golfers and knee moments were compared between conditions using repeated measures T-tests. The golf swing knee moment magnitudes were also descriptively compared to those reported for two athletic maneuvers (drop jump landing, side-step cutting) and activities of daily living (gait, stair ascent). The EXT condition decreased the peak knee adduction moment as compared to the STR condition; however, foot position had no effect on the peak knee abduction moment. Also, the magnitude of the knee adduction moments during the two activities of daily living were 9-33% smaller than those experienced during the two different golfing conditions. The drop jump landing and golf swing knee moments were of similar magnitude (STR= - 5%, EXT= + 8%); however, the moments associated with side- step cutting were 50-71% larger than those on the target side knee during the golf swing. The loading of the target side knee during the golf swing may be a factor in the development and progression of knee pathologies and further research should examine ways of attenuating these loads through exercise and swing modifications. Key pointsAn externally rotated front foot position at address would be recommended for those with medial knee pathology in the target side limb.There is a large valgus moment on the target side knee during the golf swing that is not decreased with external rotation of the foot at address.The potential of the knee moments on the target side limb to lead to knee pathologies in golfers needs to be further investigated.
As runners age, the likelihood of developing osteoarthritis (OA) significantly increases as 10% of people 55+ have symptomatic knee OA while 70% of people 65+ have radiographic signs of knee OA. The ...lateral-medial shear force (LMF) and knee adduction moment (KAM) during gait have been associated with cartilage loading which can lead to OA. Foot rotation during gait has been shown to alter the LMF and KAM, however it has not been investigated in running. The purpose of this study was to investigate changes in the KAM and LMF with foot rotation during running. Twenty participants volunteered and performed five running trials in three randomized conditions (normal foot position NORM, external rotation EXT, and internal rotation INT) at a running speed of 3.35m·s(-1) on a 20 meter runway. Kinematic and kinetic data were gathered using a 9-camera motion capture system and a force plate, respectively. Repeated measures ANOVAs determined differences between conditions. The KAM and LMF were lower in both EXT and INT conditions compared to the NORM, but there were no differences between EXT and INT conditions. The decreases in KAM and LMF in the EXT condition were expected and concur with past research in other activities. The reductions in the INT condition were unexpected and contradict the literature. This may indicate that participants are making mechanical compensations at other joints to reduce the KAM and LMF in this abnormal internal foot rotation condition. Key pointsExternal rotation of the foot during running reduced the loads on the medial compartment of the kneeInternal rotation of the foot also reduced the medial loads, but is a more unnatural interventionExternal and internal rotation reduced the shear forces on the knee, which may help slow the degeneration of knee joint cartilage.
Although running stairs is often used in sport conditioning programs, at present, little research has examined the effect of stair climb training on sprint power. The purpose of this study was to ...investigate the effects of running stairs either 1 stair (1S) or 2 stairs (2S) at a time on power. Fourteen male college track and field athletes were randomized into 3 groups; 1S, 2S, or control (C). All groups were pre- and posttested for 1S, 2S, and 40-m sprint split times. The 1S and 2S groups trained twice per week, for 4 weeks, performing 10 sets of climbing 68 total stairs with 2.5-minute rest between trials. The greatest power values (W) from pre- and poststairs and sprint splits were used for statistical analyses. There was a significant (p < 0.05) interaction of group × time for stair climb. The 1S group increased power for the 1S test (pre-1,492.89 ± 123.76; post-1,647.41 ± 73.65) with no change in the 2S test (pre-2,428.80 ± 414.81; post-2,430.32 ± 154.90), whereas the 2S group increased power for the 2S test (pre-2,343.73 ± 317.50; post-2,646.17 ± 305.43) with no change in the 1S test (pre-1,516.69 ± 210.64; post-1,529.38 ± 236.69). The C group showed no change in either stair test (1S: pre-1,403.35 ± 238.67, post-1,384.38 ± 153.32; 2S: pre-2,285.93 ± 345.03, post-2,261.85 ± 356.88). There were no significant interactions or main effects for any sprint split power (40 m: pre-5,337.13 ± 611.86, post-5,318.68 ± 586.24).Therefore, stair climb training either 1 or 2 at a time did not affect 40-m sprint split power but increased power for the specific stair training type. Coaches should choose the number of stairs that are similar in time and power output to sprint training.
