Iain Hunter

A COMPARISON OF VOLUNTARY AND INVOLUNTARY MEASURES OF ELECTROMECHANICAL DELAY

Electromechanical delay (EMD) is a measurement used to assess the mechanical lag between muscle activation onset and force production. EMD measurements may be performed by voluntary or electrically evoked muscle activation. This study compared gastrocnemius EMD during voluntary and involuntary contractions and assessd the intrasession reliability of each set of measurements. Subjects were 15 volunteers (age 21 ± 2 years, ht 171.8 ± 10.0 cm, mass 76.1 ± 13.4 kg). EMD measurements were recorded from the medial head of the gastrocnemius of each subject during voluntary and involuntary contractions. Order was counterbalanced between subjects. Subjects stood with the dominant leg on a force plate, the nondominant next to the force plate, and with their hands in contact with a bar in front of them. A supramaximal percutaneous stimulus was applied to the tibial nerve in the popliteal fossa for involuntary (electrically evoked) contractions. For voluntary contractions, subjects were instructed to rise up on the toes as quickly as possible. Four trials were collected for each condition with 30 s of rest between each. Repeated measures ANOVAs were performed for each condition to calculate an ICC (2,1). Means of the 4 trials for each condition were used to detect differences between groups. EMD was greater in the voluntary condition (22.8 ± 8.2 ms) compared to the involuntary condition (9.7 ± 3.1 ms; p < .001). Intrasession reliability for each condition was very strong (involuntary ICC (2,1) = .977; voluntary ICC (2,1) = .972). EMD measured during a single leg stance is much shorter when measured during an electrically evoked (voluntary) contraction. The difference in EMD between conditions is likely the result of differences in recruitment during the two types of contractions. Reliability within a measurement session was very strong for each of the conditions.

Whole body vibration does not potentiate the stretch reflex.

Whole body vibration (WBV) is theorized to enhance neural potentiation of the stretch reflex. The purpose of this study was to determine if WBV affects the quadriceps reflex from a patellar tendon tap. Subjects were 22 volunteers (age 23 +/- 2 yrs, ht 172.8 +/- 10.8 cm, body mass 68.6 +/- 12.3 kg). The stretch reflex was elicited from the dominant leg pre, post, and 30-min post WBV treatment. A matched control group repeated the procedure without WBV. WBV treatment consisted of 5, 1-min bouts at 26 Hz with a 1-min rest period between bouts while maintaining a standardized squatting position. Two-way ANOVAs were used to detect differences between groups over time for vastus medialis (VM) and vastus lateralis (VL) latency, EMG amplitude, electromechanical delay (EMD), and force output. No group x time interactions were detected for latency (VM; F ((2,40)) = 1.20, p = .313: VL; F ((2,40)) = 0.617, p = .544), EMG mean amplitude (VM; F ((2,40)) = 0.169, p = .845: VL; F ((2,40)) = 0.944, p = .398), EMD (VM; F ((2,40)) = 0.715, p = .495: VL; F ((2,40)) = 1.24, p = .301), or quadriceps force (F ((2,40)) = 1.11, p = .341) A single session WBV treatment does not affect the quadriceps stretch reflex in terms of timing or amplitude.

Differences in technique between sprinters and distance runners at equal and maximal speeds

In the finishing kick of a distance race, maximizing speed becomes the focus even if economy may be sacrificed. If distance runners knew how to alter their technique to become more sprint-like, this process could be more successful. In this study, we compared the differences in technique between sprinters and distance runners while running at equal and maximal speeds. Athletes consisted of 10 Division I distance runners, 10 Division I sprinters, and 10 healthy non-runners. They performed two tests, each consisting of a 60-m run on the track: Test 1 at a set pace of 5.81 m/s, while Test 2 was maximal speed. Video was collected at 180 Hz. Significant differences (P < 0.05) between the sprint and distance groups at maximal speeds were found in the following areas: speed, minimum hip angle, knee extension at toe-off, stride length, contact time, and recovery knee at touchdown. In Test 1, sprinters and distance runners displayed many of the same significant differences. The control group was similar to the distance group in both trials. As distance runners attempt to sprint, the desired adjustments do not necessarily occur. Distance runners may benefit from biomechanical interventions to improve running speed near the end of a race.

Whole-body vibration strengthening compared to traditional strengthening during physical therapy in individuals with total knee arthroplasty

ABSTRACT This study investigated the use of whole-body vibration (WBV) as an alternative strengthening regimen in the rehabilitation of individuals with total knee arthroplasty (TKA) compared with traditional progressive resistance exercise (TPRE). Individuals post TKA (WBV n = 8; TPRE n = 8) received physical therapy with WBV or with TPRE for 4 weeks. Primary dependent variables were knee extensor strength, quadriceps muscle activation, mobility, pain, and range of motion (ROM). There was a significant increase in knee extensor strength and improvements in mobility, as measured by maximal volitional isometric contraction and the Timed Up and Go Test (TUG), respectively, for both groups (p < 0.01). The WBV knee extensor strength improved 84.3% while TPRE increased 77.3%. TUG scores improved 31% in the WBV group and 32% for the TPRE group. There were no significant differences between groups for strength or muscle activation (Hotellings T2 = 0.42, p = 0.80) or for mobility (F = 0.54; p = 0.66). No adverse side effects were reported in either group. In individuals with TKA, both WBV and TPRE showed improved strength and function. Influence of WBV on muscle activation remains unclear, as muscle activation levels were near normal for both groups.

Reflex inhibition of electrically induced muscle cramps in hypohydrated humans.

INTRODUCTION Anecdotal evidence suggests that ingesting small volumes of pickle juice relieves muscle cramps within 35 s of ingestion. No experimental evidence exists supporting the ingestion of pickle juice as a treatment for skeletal muscle cramps. METHODS On two different days (1 wk apart), muscle cramps were induced in the flexor hallucis brevis (FHB) of hypohydrated male subjects (approximately 3% body weight loss and plasma osmolality approximately 295 mOsm x kg(-1) H2O) via percutaneous tibial nerve stimulation. Thirty minutes later, a second FHB muscle cramp was induced and was followed immediately by the ingestion of 1 mL x kg(-1) body weight of deionized water or pickle juice (73.9 +/- 2.8 mL). RESULTS Cramp duration and FHB EMG activity during the cramp were quantified, as well as the change in plasma constituents. Cramp duration (water = 151.9 +/- 12.9 s and pickle juice = 153.2 +/- 23.7 s) and FHB EMG activity (water = 60% +/- 6% and pickle juice = 68% +/- 9% of maximum voluntary isometric contraction EMG activity) were similar during the initial cramp induction without fluid ingestion (P > 0.05). During FHB muscle cramp induction combined with fluid ingestion, FHB EMG activity was again similar (water = 55% +/- 9% and pickle juice = 66% +/- 9% of maximum voluntary isometric contraction EMG activity, P > 0.05). However, cramp duration was 49.1 +/- 14.6 s shorter after pickle juice ingestion than water (84.6 +/- 18.5 vs 133.7 +/- 15.9 s, respectively, P < 0.05). The ingestion of water or pickle juice had little impact on plasma composition 5 min after ingestion. CONCLUSIONS Pickle juice, and not deionized water, inhibits electrically induced muscle cramps in hypohydrated humans. This effect could not be explained by rapid restoration of body fluids or electrolytes. We suspect that the rapid inhibition of the electrically induced cramps reflects a neurally mediated reflex that originates in the oropharyngeal region and acts to inhibit the firing of alpha motor neurons of the cramping muscle.

EMG activity during positive-pressure treadmill running

Success has been demonstrated in rehabilitation from certain injuries while using positive-pressure treadmills. However, certain injuries progress even with the lighter vertical loads. Our purpose was to investigate changes in muscle activation for various lower limb muscles while running on a positive-pressure treadmill at different amounts of body weight support. We hypothesized that some muscles would show decreases in activation with greater body weight support while others would not. Eleven collegiate distance runners were recruited. EMG amplitude was measured over 12 lower limb muscles. After a short warm-up, subjects ran at 100%, 80%, 60%, and 40% of their body weight for two minutes each. EMG amplitudes were recorded during the final 30s of each stage. Most muscles demonstrated lower amplitudes as body weight was supported. For the hip adductors during the swing phase and the hamstrings during stance, no significant trend appeared. Positive-pressure treadmills may be useful interventions for certain injuries. However, some injuries, such as hip adductor and hamstring tendonitis or strains may require alternative cross-training to relieve stress on those areas. Runners should be careful in determining how much body weight should be supported for various injuries to return to normal activity in the shortest possible time.

Whole body vibration as an adjunct to static stretching.

This study was a randomized control trial. The purpose of this study was twofold: 1) to determine if stretching the hamstrings during whole-body-vibration (WBV) is more effective than static stretching alone; and 2) to monitor retention of flexibility changes. The main outcome measure was hamstring flexibility as measured in degrees using a passive knee extension test. Thirty-four recreationally active college-age subjects (23.4+/-1.7 yrs) completed this study (22 males, 12 females, avg. ht.=175.6+/-6.4 cm, avg. wt.=74.9+/-11.8 kg). Subjects were assigned to a control group (C), a static stretch group (SS), or a vibration + static stretch group (V). Subjects stretched 5 days/wk for 4-weeks and were followed for 3-weeks after cessation to monitor retention. Analysis showed a significant difference between treatment groups (p<0.0001), time (p<0.0001), gender (p=0.0002) and in treatment*time (p=0.0119), with 14%+/-3.86% (SEM) and 22%+/-3.86% (SEM) increases in flexibility after 4-weeks of stretching for the SS and V groups respectively. Three-week follow-up showed SS returning to baseline with V group still 6.4 degrees (11%+/-3.88% (SEM)) more flexible than at baseline. Stretching concurrently with vibration on a WBV platform appears to be a good adjunct to static stretching with the potential to enhance retention of flexibility gains.

The effects of external ankle support on dynamic restraint characteristics of the ankle in volleyball players.

Objective:To examine any changes in electromechanical delay and reaction time as a result of the use of external ankle supports over an entire season (3-5 months) in college volleyball players. Design:A 2 × 3 pre-post factorial design. Setting:Biomechanics laboratory, Human Performance Research Center. Participants:Thirty healthy, active male and female intercollegiate volleyball players were recruited for this study (age, 20.4 ± 2.3 years; height, 183.1 ± 8.6 cm; weight, 74.0 ± 9.5 kg). Interventions:External supports consisted of the subjects wearing either tape or braces for practices and games for the duration of the volleyball season. Subjects in the control group wore nothing on their ankles for practices and games for the duration of the volleyball season. Main Outcome Measures:The electromechanical delay (EMD) of the peroneus longus was determined by the onset of force contribution after artificial activation, as measured by electromyographic (EMG) and forceplate data. Reaction time was measured after an inversion perturbation during walking. Results:No significant (F2,27 = 0.141, P = 0.869) interaction was observed for reaction time between the groups over time. No significant (F2,27 = 0.236, P = 0.791) interaction was observed for EMD between groups over time. Conclusion:Use of an external ankle support over an entire season does not induce neuromuscular changes in the onset timing of the peroneus longus.

Water treadmill parameters needed to obtain land treadmill intensities in runners.

PURPOSE To establish water treadmill running parameters with shoes (WTR-S) and without water shoes (WTR-NS) needed to obtain known land treadmill running (LTR) cardiorespiratory responses. METHODS Eighteen trained college-aged runners participated in three running conditions (LTR, WTR-S, and WTR-NS) where cardiorespiratory responses were measured. The primary variables of interest were VO2, HR, treadmill speed, and stride frequency (SF). These variables were assessed at 50%, 60%, 70%, and 80% equivalents of land VO2max for all three running conditions. RESULTS Data were centered; so in the analysis, intercepts were calculated within the range of data. At an HR of 150 bpm, VO2 was significantly less (P < 0.05) during LTR (34.6 mL·kg(-1)·min(-1)) compared with WTR-S (37.5 mL·kg(-1)·min(-1)) and WTR-NS (37.2 mL·kg(-1)·min(-1)). HR was approximately 7 bpm less during WTR compared with LTR, although the metabolic demand (VO2) was similar. At a treadmill speed of 160.9 m·min(-1), SF during LTR was 23.6 strides per minute greater (P < 0.05) than that during WTR-S and 21.8 strides per minute greater than that during WTR-NS. Wearing water shoes increased VO2 by 4.12 mL·kg(-1)·min(-1) at any given water treadmill speed. CONCLUSIONS To achieve metabolic oxygen demands equivalent to intensities from 50% to 80% of VO2max on LTR, WTR parameters have to be changed from those used on LTR. WTR is an effective alternative to LTR. Subjects were able to exercise on the water treadmill at intensities equivalent to 80% of their VO2max and 55% to 94% of their land HRmax. Individuals can select a treadmill speed during WTR that elicits an HR of approximately 7 bpm less than their LTR to obtain a cardiorespiratory overload equivalent to 50%, 60%, 70%, and 80% of their land VO2max.

Ambulation speed and corresponding mechanics are associated with changes in serum cartilage oligomeric matrix protein.

Because serum cartilage oligomeric matrix protein (COMP) has been used to reflect articular cartilage condition, we aimed to identify walking and running mechanics that are associated with changes in serum COMP. Eighteen subjects (9 male, 9 female; age=23 ± 2 yrs.; mass=68.3 ± 9.6 kg; height=1.70 ± 0.08 m) completed 4000 steps on an instrumented treadmill on three separate days. Each day corresponded to a different ambulation speed: slow (preferred walking speed), medium (+50% of slow), and fast (+100% of slow). Synchronized ground reaction force and video data were collected to evaluate walking mechanics. Blood samples were collected pre-, post-, 30-minute post-, and 60-minute post-ambulation to determine serum COMP concentration at these times. Serum COMP increased 29%, 18%, and 5% immediately post ambulation for the fast, medium, and slow sessions (p<0.01). When the speeds were pooled, peak ankle inversion, knee extension, knee abduction, hip flexion, hip extension, and hip abduction moment, and knee flexion angle at impact explained 61.4% of total variance in COMP concentration change (p<0.001). These results indicate that (1) certain joint mechanics are associated with acute change in serum COMP due to ambulation, and (2) increased ambulation speed increases serum COMP concentration.