Vertical jump and short distance sprints (
Jumping and sprint performance is dependent upon the synchronized contribution of force and power from each leg. It is known that the combined effort from each leg is not as great as the sum of each leg measured individually (Bobbert et al., 2006; Taniguchi, 1998). Yet, the magnitude and direction of each leg's force and power is combined to produce a single, linear force/power vector (McGinnis, 2013). Therefore, a vertical jump or linear sprint may suffer from sub-optimal linear propulsion if these forces are unequal or misaligned. Recently, Bell and colleagues (2014) demonstrated relationships between lower limb lean mass asymmetry and asymmetrical jumping force and power (Bell et al., 2014). However, this particular investigation only examined the effect these asymmetries had on maximal jumping height. No study has looked into the effect of asymmetrical muscle architecture (e.g. pennation angle and fascicle length), muscle size, or muscle quality on absolute jumping power or sprinting speed.
To a certain degree, skeletal muscle architecture and its activation are both responsible for the resultant production of force and power (Hoffman, 2006). The manner in which muscle architecture and activation affect force and power may be influenced by physical activity, training status, and gender. During puberty, skeletal structure and circulating testosterone, which affect muscle strength and development, differ significantly between men and women (Komi and Bosco, 1978; Komi and Karlsson, 1978; Saladin, 2009). As a result, absolute differences in strength, rate of force development, explosive capability, muscle recruitment, and muscular symmetry have been previously documented between genders (Hewitt et al., 1999; Komi and Bosco, 1978; Komi and Karlsson, 1978; Lawson et al., 2006; Rodano et al., 1996). It is possible that the manner in which muscle architecture affects vertical jumping and sprinting performance may also vary by gender. Therefore, the purpose of the present investigation was to determine the influence of gender and muscle architecture asymmetry on vertical jump power and short-distance sprinting speed.
The relationships between skeletal muscle architecture, as measured by ultrasound, and athletic field tests (vertical jump & 30m sprint) were assessed in physically active men and women. Participants reported to the Human Performance Laboratory on three separate occasions. On the first visit (T1), eligible participants were advised of the purpose, risks and benefits associated with the study. After providing their informed consent, body composition was measured in all eligible participants. Within 1-2 days of T1, participants returned for the second visit (T2), during which a standardized warm-up preceded the assessment of vertical jump height and power. The final visit (T3) occurred within one week from T2. Following ultrasound measurements of the right and left leg thigh musculature (rectus femoris and vastus lateralis), the participants completed three maximal 30-m sprints. The Institutional Review Board of the University approved this research protocol.
Twenty-eight healthy, physically active men (n = 14) and women (n = 14) (Table 1), volunteered to participate in this study. Participants completed a health and physical activity questionnaire, Physical Activity Readiness Questionnaire (PAR-Q), and an informed consent prior to participation. All participants were free of any physical limitations and had been recreationally active (exercised 2-3 times per week).
During T1, height ([+ or -] 0.1cm) and body mass ([+ or -] 0.1kg) were measured using a Health-o-meter Professional scale (Patient Weighing Scale, Model 500 KL, Pelstar, Alsip, IL, USA). Skinfold measurements were collected by the same investigator with skinfold calipers (Caliper-Skinfold-Baseline, Model #MDSP121110, Medline, Mundelein, IL, USA) using standardized procedures for measurement of the triceps, suprailiac, abdomen, and thigh (Hoffman, 2006). Previously published formulas were used to calculate body fat percentage (%FAT) (Jackson and Pollock, 1985).
Vertical jump assessment
Following a 5-min warm-up on a cycle ergometer, vertical jump height was measured using a Vertical Jump Testing station (Uesaka Sport, Colorado Springs, CO) during T2. Before testing, standing vertical reach height was determined by colored squares located along the vertical neck of the device. Each square corresponded with similarly colored markings on each horizontal tab, which indicated the vertical distance (in inches) from the associated square. Vertical jump (VJ) height was determined by the indicated distance on the highest tab reached following 3 maximal countermovement jump attempts and in accordance with previously described procedures (Hoffman, 2006). Peak (PVJP) and mean (MVJP) vertical jump power were determined from a TendoTM Weightlifting Analyzer (Tendo Sports Machines, Trencin, Slovakia) that was attached at the participant's waist during the vertical jump assessment. The Tendo[TM] unit consists of a transducer that measured velocity (m * [s.sup.-1]), defined as linear displacement over time. Power (W) was calculated by multiplying vertical jump velocity and the participant's body mass. PVJP and MVJP were recorded for each jump and used for subsequent analysis. The ICCs for PVJP and MVJP, as measured by the Tendo [TM] unit in our laboratory, are 0.98 (SEM = 106.2 W) and 0.94 (SEM = 100.3 W), respectively.
Measurements of muscle architecture
Prior testing on T3, participants reported to the laboratory and laid supine for 15 minutes to allow fluid shifts to occur before the collection of ultrasound images (Berg et al., 1993). Subsequently, non-invasive skeletal muscle ultrasound images were collected from the rectus femoris (RF) and vastus lateralis (VL). A 12 MHz linear probe scanning head (General Electric LOGIQ P5, Wauwatosa, WI, USA) was used to optimize spatial resolution and was coated with water soluble transmission gel and positioned on the surface of the skin to provide acoustic contact without depressing the dermal layer to collect the image. All measures were taken in both the RF and VL of both legs and performed by the same technician. The anatomical location for all ultrasound measures was standardized for each muscle in all participants. For measures of RF, the participant was placed supine on an examination table, according to the American Institute of Ultrasound in Medicine, with the legs extended but relaxed and with a rolled towel beneath the popliteal fossa allowing for a 10[degrees] bend in the knee as measured by a goniometer (Scanlon et al., 2014). For measures of the VL, the participant was placed on their side with the legs together and relaxed allowing for a 10[degrees] bend in the knee as measured by a goniometer. Following scanning, all images were analyzed offline using ImageJ (National Institutes of Health, Bethesda, MD, USA, version 1.45s), an image analysis software available through the National Institute of Health. For these analyses, a known distance of 1cm shown in the image was used to calibrate the software program (Scanlon et al., 2014).
Measures of muscle...