Scott K. Lynn

Effect of foot rotation on knee kinetics and hamstring activation in older adults with and without signs of knee osteoarthritis.

BACKGROUND To determine the effects of changing the natural foot progression angle during gait (internal and external foot rotation) on the knees adduction moment, lateral-medial shear force, and the ratio of medial-lateral hamstring muscle activation in those with signs of knee osteoarthritis and a matched healthy control group. METHODS Twelve subjects with signs of knee osteoarthritis and 12 matched healthy control subjects were evaluated. A 3D gait analysis system calculated forces and moments at the knee while the subjects walked in three conditions: (1) normal foot position, (2) external foot rotation, (3) internal foot rotation. Medial and lateral hamstring EMG data was also collected simultaneously and used to calculate the medial-lateral hamstring activation ratio during the stance phase of the gait cycle. Repeated measures ANOVAs were used to compare foot rotation conditions within each group; while between group comparisons were performed in the normal rotation condition only using t-tests. FINDINGS Those with knee osteoarthritis (OA) had an increased late stance knee adduction moment and a decreased medial-lateral hamstring activation ratio as compared to the healthy control group. Also, external foot rotation decreased the late stance knee adduction moment, lateral-medial shear force, and hamstring activation ratio. However, internal foot rotation did not increase these measures. INTERPRETATION Changes in foot position during gait have the ability to alter both the external loading of the knee joint and hamstring muscle activation patterns during gait. This may have implication in helping to unload the knees articular cartilage.

Lower Extremity Biomechanics During a Regular and Counterbalanced Squat

Abstract Lynn, SK and Noffal, GJ. Lower extremity biomechanics during a regular and counterbalanced squat. J Strength Cond Res 26(9): 2417–2425, 2012—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.

Bench Press Upper-Body Muscle Activation Between Stable and Unstable Loads.

Abstract Dunnick, DD, Brown, LE, Coburn, JW, Lynn, SK, and Barillas, SR. Bench press upper-body muscle activation between stable and unstable loads. J Strength Cond Res 29(12): 3279–3283, 2015—The bench press is one of the most commonly used upper-body exercises in training and is performed with many different variations, including unstable loads (ULs). Although there is much research on use of an unstable surface, there is little to none on the use of an UL. The purpose of this study was to investigate muscle activation during the bench press while using a stable load (SL) vs. UL. Twenty resistance-trained men (age = 24.1 ± 2 years; ht = 177.5 ± 5.8 cm; mass = 88.7 ± 13.7 kg) completed 2 experimental conditions (SL and UL) at 2 different intensities (60 and 80% one repetition maximum). Unstable load was achieved by hanging 16 kg kettlebells by elastic bands from the end of the bar. All trial lifts were set to a 2-second cadence with a slight pause at the bottom. Subjects had electrodes attached to 5 muscles (pectoralis major, anterior deltoid, medial deltoid, triceps brachii, and latissimus dorsi) and performed 3 isometric bench press trials to normalize electromyographic data. All 5 muscles demonstrated significantly greater activation at 80% compared with 60% load and during concentric compared with eccentric actions. These results suggest that upper body muscle activation is not different in the bench press between UL and SL. Therefore, coaches should use their preference when designing training programs.

Biomechanics of Power in Sport

SUMMARY SUCCESS IN MANY ATHLETIC AND SPORTING ACTIVITIES MAY BE ENHANCED BY THE ABILITY TO OPTIMIZE MUSCULAR POWER OUTPUT. THIS ARTICLE WILL PRESENT THE BIOMECHANICAL DEFINITIONS, CHARACTERISTICS, AND APPLICATIONS OF POWER IN SPORT.

Progressions of Isometric Core Training

ABSTRACT WITH THE GROWTH IN POPULARITY OF CORE TRAINING, IT IS IMPORTANT THAT THERE IS A CLEAR UNDERSTANDING OF HOW TO BEST TAILOR THESE EXERCISES TO SAFELY MEET THE NEEDS OF DIFFERENT INDIVIDUALS. EXTENSIVE RESEARCH HAS SHOWN THAT TRAINING THE CORE MUSCLES ISOMETRICALLY, THAT IS WITHOUT BENDING THE SPINE, IS SAFE AND MAY HELP REDUCE THE INCIDENCE OF BACK INJURY. EXERCISE PROFESSIONALS MUST HAVE THE ABILITY TO MODIFY ISOMETRIC CORE EXERCISES AND ALTER THEIR DIFFICULTY TO ENSURE THAT THEY PROVIDE A SAFE AND APPROPRIATE CHALLENGE FOR INDIVIDUALS OF VARYING FITNESS LEVELS AND TRAINING GOALS. THEREFORE, THIS ARTICLE SUMMARIZES THE CURRENT RESEARCH THAT OUTLINES THE POTENTIAL NEGATIVE CONSEQUENCES OF CONSTANTLY BENDING OR MOVING THROUGH THE SPINE. THIS PROVIDES THE RATIONALE FOR TRAINING THE CORE ISOMETRICALLY TO AVOID REPLICATING THESE KNOWN MECHANISMS OF INJURY DURING EXERCISE. EXAMPLES OF ISOMETRIC CORE EXERCISES OF VARYING DIFFICULTY ARE ALSO PROVIDED, AS WELL AS A MODEL OUTLINING HOW TO IMPLEMENT THESE PROGRESSIONS TO SAFELY MEET THE NEEDS OF ANY INDIVIDUAL IN A GENERAL FITNESS POPULATION.

Electromyographic and Force Plate Analysis of the Deadlift Performed With and Without Chains

Abstract Nijem, RM, Coburn, JW, Brown, LE, Lynn, SK, and Ciccone, AB. Electromyographic and force plate analysis of the deadlift performed with and without chains. J Strength Cond Res 30(5): 1177–1182, 2016—The purpose of this study was to determine the effects of deadlift chain variable resistance on surface electromyography (EMG) of the gluteus maximus, erector spinae, and vastus lateralis muscles, ground reaction forces (GRFs), and rate of force development (RFD). Thirteen resistance-trained men (24.0 ± 2.1 years, 179.3 ± 4.8 cm, 87.0 ± 10.6 kg) volunteered for the study. On day 1, subjects performed 1 repetition maximum (1RM) testing of the deadlift exercise. On day 2, subjects performed one set of 3 repetitions with a load of 85% 1RM with chains (CH) and without chains (NC). The order of the CH and NC conditions was randomly determined for each subject. For the CH condition, the chains accounted for approximately 20% (19.9 ± 0.6%) of the 85% 1RM load, matched at the top of the lift. Surface EMG was recorded to differentiate muscle activity between conditions (CH, NC), range of motion (ROM; bottom, top), and phase (concentric, eccentric). Peak GRFs and RFD were measured using a force plate. Electromyography results revealed that for the gluteus maximus there was significantly greater EMG activity during the NC condition vs. the CH condition. For the erector spinae, EMG activity was greater at the bottom than the top ROM (p ⩽ 0.05). Force plate results revealed that deadlifting at 85% 1RM with an accommodating chain resistance of approximately 20% results in a reduction in GRFs (p ⩽ 0.05) and no change in RFD (p > 0.05). Collectively, these results suggest that the use of chain resistance during deadlifting can alter muscle activation and force characteristics of the lift.

Effect Of Foot Rotation During Running On Knee Moments And Lateral-medial Shear Force: 2984 Board #270 May 30, 3

Approximately 10%-20% of Americans run for recreational purposes on a regular basis (6). Currently, there are running races which have over 40,000 people participating (27) while in 1960, marathon races struggled to get 1,000 participants (6), which serves as a statement of illustration for the growth of running as a recreational sport. The health benefits of running continue to draw in new runners, but the increasing incidence of injuries leaves some runners and aspiring runners questioning the sport. The knee joint is the most common site for a running related injury (21). Osteoarthritis (OA) is a commonly occurring pathology in older adults with 10% of people over 55 experiencing symptomatic knee OA, while there are signs of radiographic knee OA in 70% of people over the age of 65 (17). This high prevalence of knee OA is thought to be due to improper loading of the knee over many years (18). Since approximately 17% of male runners and 6% of female runners are over the age of 56, it stands to reason that a good portion of the running community is at risk for OA.