EFFECT OF AN ANKLE COMPRESSION GARMENT FATIGUE AND PERFORMANCE NEMANJA Sˇ AMBAHER, SAIED J. ABOODARDA, DUSTIN B. SILVEY, DUANE C. BUTTON, DAVID G. BEHM

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School of Human Kinetics and Recreation, Memorial University of Newfoundland, St. John’s, Newfoundland, Canada ABSTRACT

INTRODUCTION

ˇ Sambaher, N, Aboodarda, SJ, Silvey, DB, Button, DC, and Behm, DG. Effect of an ankle compression garment on fatigue and performance. J Strength Cond Res 30(2): 326–335, 2016— The aim of this study was to examine the effects of an ankle compression garment (CG) on muscle performance and physiological variables associated with recovery from fatigue. Fifteen participants took part in a randomized crossover study design with 2 experimental conditions (ankle CG and control). The dependent variables skin temperature, evoked muscle contractile properties, maximal voluntary contraction (MVC) force, electromyography (EMG), drop jump performance (20, 35, and 50 cm box heights), continuous drop jump (30 cm), time to fatigue (TTF), and blood lactate concentration were measured pre- and post-warmup and postfatigue. Compared with control condition, ankle CG condition had significantly reduced half-relaxation times (p = 0.043) and higher skin temperatures at post-warm-up and postfatigue protocol (p , 0.001, D3.2 and D4%, respectively). Participants also exhibited significantly lower ground reaction forces (GRFs) for 50-cm drop jumps (p = 0.044, D9.9%) with ankle CG at post-warm-up. There were no significant differences between conditions for muscle contractile properties, MVC force or EMG, jump height, take-off velocity, contact time, and jumping TTF. Independent of group, there was a threefold increase in blood lactate (p , 0.01) from pre-warm-up to post-fatigue and a significant decrease in MVC force (p = 0.048, D8.1%) from postwarm-up to postfatigue. Results suggest that ankle CG increased and maintained skin temperature during recovery, decreased twitch half-relaxation times, and reduced GRF from a 50-cm drop height. However, ankle CG did not improve other performance measures, aid in recovery, or affect blood lactate clearance.

KEY WORDS compression sleeve, maximal voluntary contraction, blood lactate, evoked contractions, jumps, temperature Address correspondence to David G. Behm, [email protected]. 30(2)/326–335 Journal of Strength and Conditioning Research Ó 2016 National Strength and Conditioning Association

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ompression garments (CGs), such as full body suits, tights, tops, stockings, and ankle compression sleeves, are widely used in the fitness and sports community. Athletes and fitness enthusiasts are using CGs to increase sport performance (26), enhance recovery (25,28), prevent injury, and reduce chafing (14). However, it is difficult to extrapolate the research findings from CG studies because CGs vary greatly in shape, size, material, and compression intensity (31) and are used on different muscles and joints. One consistent research finding on the effect of CGs is increased skin temperature (17,24). Skin temperature has been shown to positively correlate with muscle temperature (10). Increased muscle temperature may lead to increased muscle power and force (40) and muscle twitch force and rate of twitch force development (15,18). Compression garments reduced the decline in evoked muscle twitch force after a plantar flexor fatiguing exercise (33). However, studies have shown that muscle heating did not increase elbow (34) or plantar (37) flexors maximal voluntary contraction (MVC), and Duffield et al. (16) reported that CG was not able to attenuate the decline in evoked twitch force after intermittent sprint and plyometric exercise. Preventing muscle temperature drop after a warm-up may also be important for muscle performance. Maintenance of muscle temperature would be important in cold environmental conditions, which are known to reduce MVC force, twitch force, and tetanic force (15). Faulkner et al. (20) showed that keeping muscles warm after a sprint-specific cycling caused a greater peak power output (z9%) during a 30-second maximal cycling sprint compared with control. Compression garments may increase skin temperature subsequently increasing muscle temperature or prevent muscle temperature drop during periods of inactivity ultimately leading to enhanced muscular performance. However, this effect has not been fully documented and what is documented seems to be conflicting. It has been suggested that CGs can enhance jumping performance through a coupling of the fabric recoil and compression exerted around the limbs, thereby increasing proprioception and aiding the stretch-shortening cycle (SSC) (27,39). Compression garments can improve repeated 30-m sprint times (9), single maximal vertical jump power

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Journal of Strength and Conditioning Research output (14), increase repetitive countermovement jump performance (26,27), maintain countermovement jumping performance after running fatigue (39), and lessen the decline in squat jump performance and isokinetic muscle strength (25). However, conflicting studies have reported that CGs did not affect countermovement jump performance (25), maximal voluntary plantar flexion torque (33), 20-m shuttle run test (4) sprint performance (14,16,23,24), and running time to fatigue (TTF) (38). To the best of our knowledge, there are no studies investigating whether CGs can enhance repetitive drop jump performance until task failure (jumping TTF) and lessen the impact of fatigue on subsequent drop jump performance. In addition, no studies have specifically measured whether CGs can alleviate the decline of maximal force generating capability of ankle plantar flexors after a fatiguing task. Surface electromyography (EMG) has been used as a means to investigate possible ergogenic effects of CGs. Born et al. (9) found that CG increased rectus femoris EMG, which may be associated with increased 30-m sprint performance. Fu et al. (21) found decreased muscle activity during maximum knee extensor torque and power output with CG compared with without CG, which might indicate increased neuromuscular efficiency. Passively increasing skin temperature also increases neuromuscular efficiency during plantar flexor MVC (37). Miyamoto et al. (33) found a smaller decrement in EMG mean power frequency during ankle plantar flexor MVC with CG, indicating that there was less muscle fatigue when wearing CG. Investigating EMG before and after a jumping task to failure may reveal more possible ergogenic effects of CGs on neuromuscular function. Lactate accumulation proportionally increases with other metabolites that disrupt excitation-contraction coupling (e.g., inorganic phosphate) during strenuous physical activity, thereby affecting muscle performance (29). Compression garments have decreased blood lactate levels after highintensity running and cycling exercise (12,30). Compression garment–induced lower blood lactate values could be due to increased blood flow (7,8) (i.e., attributed to an augmentation of the muscle pump), lower lactate production, or muscle retention of lactate (7). However, Higgins et al. (23) found increased netball-specific physical performance with CG, but no significant changes for blood lactate levels. Similarly, Duffield et al. (16) found no CG-induced changes in lactate during sprinting and bounding performance. The discrepancies in the literature associated with the effect of CGs on blood lactate levels suggest more research is needed. To our knowledge, few studies have examined the effect of CGs on (a) repetitive jump performance and (b) skin temperature and voluntary and evoked muscle contractile properties before and after a fatiguing task. Therefore, the aim of this study was to examine the effects of CG on neuromuscular (voluntary isometric contractions, evoked contractile properties, EMG, drop jumps) performance, blood lactate, and skin temperature before and after fatigue.

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It was hypothesized that CG would induce higher skin temperatures after the warm-up and maintain higher skin temperatures postexercise. Furthermore, it was hypothesized that the CG would contribute to lower blood lactate, leading to increases in performance and significantly lesser fatiguerelated impairments in voluntary and evoked muscle contractile properties.

METHODS Experimental Approach to the Problem

A repeated-measures, randomized, crossover study design was used, with 1 familiarization session (introduced and sized CG, and practiced fatigue intervention and testing procedures with CG) and 2 experimental sessions separated by 48–96 hours. Only the experimental sessions were randomly assigned. The effects of wearing below-knee graduated ankle CG on skin temperature, evoked muscle contractile properties, MVC force, ankle plantar flexors EMG activity, drop jump performance, jumping TTF (30-cm platform), and blood lactate clearance in a recreationally trained population were examined. These measurements were repeated pre-warm-up, 10 minutes post-warm-up (to allow the muscle to cool post-warm-up), and post-fatigue. Warm-up consisted of bicycling for 5 minutes at 70 rpm and 1 kilopond (kP) resistance, 20 calf raises, and 30 hops. The time of the day that the participant was tested remained consistent for both testing sessions. All tests were performed in ambient temperate conditions (z228 C and 35% relative humidity) and were kept constant across testing sessions. During testing, all participants received verbal encouragement by the same investigator and continuous feedback on achievement. There was no specific advice regarding nutrition, but they were advised to eat a similar meal before each testing session. Subjects

Based on a priori statistical power analysis of related articles (13,26) to achieve an alpha of 0.05 and a power of 0.8, 15 healthy, active participants (age range 19–30 years) were recruited for the study. The participants’ characteristics were as follows: women (n = 8) 22.3 6 1.5 years, 165.6 6 3.6 cm, 60.7 6 3.5 kg and men (n = 7) 24.8 6 4.2 years, 178.3 6 9.3 cm, 76.8 6 9.8 kg. All participants acted as their own controls and were university students, who were involved in regular physical activity such as resistance training and running (at least 3– 5 days per week). None of the participants were specifically drop jump trained, but had drop jump experience. None of the participants had worn CG on a regular or consistent basis. Participants were requested to avoid training the day before the testing days. All participants completed a Physical Activity Readiness Questionnaire form from the Canadian Society for Exercise Physiology (11). Participants were verbally informed of the purpose, procedures, and risks associated with the study, their freedom to withdraw at any time without prejudice, and if they agreed, they signed the consent form. Ethical VOLUME 30 | NUMBER 2 | FEBRUARY 2016 |

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Compression Effects on Fatigue and Performance approval for the study was granted by the Institutional Health Research Ethics Authority (HREB 14 024). Protocol

During the familiarization session, participants were familiarized with the equipment and experimental procedures and all anthropometric measurements were taken. During experimental sessions 1 and 2, blood lactate, MVC force, EMG, and evoked muscle contractile properties were measured from the dominant leg (defined as the one used during the push-off phase during a jump) at pre-warm-up, post-warm-up, and post-fatigue protocol. Drop jump performance was measured post-warm-up and post-fatigue protocol. On arrival to the laboratory, pre-warm-up measures were obtained. Depending on the experimental session, participants either put on an ankle CG (ankle CG condition) or performed the rest of the testing session in ankle high socks (control condition). After the addition of the CG or ankle sock, participants proceeded to the warm-up, which consisted of bicycling for 5 minutes at 70 rpm and 1 kP resistance, 20 calf raises, and 30 hops. Once the warm-up was completed, they returned to the boot apparatus and rested for 10 minutes to induce cooling down of the muscles. From a previous pilot study without CG, it was found that 10 minutes of quiet rest after the warm-up procedure was enough to reduce skin temperature to pre-warm-up values. With this rest period, we tried to simulate the breaks that naturally occur in sport (e.g., tournament-like setting; halftime recovery period) and to investigate if CG could prevent temperature dissipation and whether this could be associated with any performance benefits at the post-warm-up or post-fatigue protocol compared with pre-warm-up. After the 10-minute rest, participants proceeded to the post-warm-up measures. Post-warm-up measures were the same as prewarm-up measures, but with the addition of drop jumps from 20-, 35-, and 50-cm platform height. Drop jump measures were performed after the warm-up, as we did not want to put the participant at risk to induce an injury with high drop jumps (i.e., 50 cm) without a proper warm-up. It was felt that other measures, such as evoked contractile properties, blood lactate, and skin temperature were more sensitive measures that would be affected by a warm-up and thus were monitored before and after the warm-up. Once the participants performed the post-warmup measurements, they proceeded to the fatiguing protocol. Post-fatigue measures (the exact same as the post-warm-up measure) were collected immediately after the fatigue protocol (see Figure 1 for a summary of the experimental procedures).

Figure 1. Experimental design and procedures. CG = compression garment; MVC = maximal voluntary contraction.

Experimental Conditions

Ankle Compression Garment Vs. Control. For the control condition, participants performed all measures in ankle high socks, whereas for the ankle CG condition, participants performed the exact same measurements while wearing Cramer ESS ankle compression sleeves (Cramer Sports

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Medicine, Gardner, KS, USA). These ankle CGs were made of 79% nylon, 20% spandex, and 1% other materials, provide graduated compression with the highest pressure at the ankle (z20–30 mm Hg), and the lowest at the knee (70% or lower of that at the ankle; Cramer products, Robert

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Journal of Strength and Conditioning Research Mogolov, personal communication, December 2014). According to the manufacturer’s instructions, we measured calf muscle girth at the widest point for participants and asked their shoe size information, which were all used to find the appropriate ankle CG size for each participant (Figure 2). Fatigue Protocol. The fatigue protocol was the same as used in a previous study from this laboratory (41). The protocol consisted of continuous drop jumps from a 30-cm platform at 70 Hz in accordance with a metronome. Time to task failure (TTF) (jumping TTF) was measured. During the fatigue protocol, participants were instructed to focus on ankle joint movement. Participants performed drop jumps until jump height, rhythm of the metronome or adequate technique could no longer be maintained. Measures

Blood Lactate. Blood lactate was collected and analyzed from the index finger using Lactate Pro (Arkray, Kyoto, Japan). Evoked Muscle Contractile Properties, Maximal Voluntary Contraction, and Electromyography. Participants were seated in a straight back chair where they secured one of their legs in a modified “boot” apparatus (Technical Services, Memorial University of Newfoundland) with hip, knee, and ankle at 908. This device has been previously shown to be valid and reliable in a number of studies from this laboratory (5,6). Evoked stimulation (Digitimer Stimulator Model DS7AH, Hertfordshire, United Kingdom) of the tibial nerve was used to obtain muscle contractile properties: peak twitch force, time to peak twitch, and twitch half-relaxation time. The cathode electrode was located in the popliteal cavity superficial to the posterior tibial nerve, whereas the anode was placed distal to the patella. The amperage of a 400-V and 200-ms pulse duration evoked stimulus was raised progressively (10-mA increment) until there was no visible increase

Figure 2. Photograph of ankle compression garment (stockings) on landing on the force plate from a depth jump.

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in peak twitch force. Peak twitch force amplitude was measured peak to peak (6). Time to peak twitch was measured as the time it took for the signal to reach the peak value from the baseline. Half-relaxation time was measured as the time the tension decreased to half of the peak twitch force value (6). Evoked muscle contractile properties were measured for 2 trials at pre-warm-up, post-warm-up, and post-fatigue protocol with 5-second interstimulus interval. Two trials were taken to ensure consistency of the data and were expressed as average of 2 trials, thereby providing 1 data point for each—prewarm-up, post-warm-up, and post-fatigue protocol. In the same straight back chair, the evoked muscle contractile property measurements were followed by 5second ankle plantar flexor MVC in the boot apparatus. Maximal voluntary contraction was measured at pre-warmup, post-warm-up, and post-fatigue, right after obtaining evoked muscle contractile properties. Straps and braces prevented extraneous movements of the upper and lower leg and securely restrained the foot so that any attempt to dorsi-flex and plantar-flex the ankle joint resulted in an isometric contraction. The device was calibrated before each session by hanging known weights off the footplate. Participants were instructed to contract as hard and as fast as possible (to reach their maximal force in the shortest time possible), while receiving constant verbal encouragement and visual feedback from the monitor in front of them. The mean force for each MVC was determined over a 1.5-second window defined as 0.75 seconds before and after the peak force of each contraction. In addition, peak force produced during first 100 milliseconds of the MVC (F100) was measured and analyzed similarly as the MVC and evoked muscle contractile properties. Electromyographic activity of 3 leg muscles (soleus [SOL], gastrocnemius medialis [GM], tibialis anterior [TA]) was recorded during the MVCs using a data acquisition system (DA USA100: analog-digital converter MP150WSW; Biopac System, Inc., Holiston, MA, USA). All EMG signals were recorded with sampling rate of 2,000 Hz using a commercially designed software program (AcqKnowledge III; Biopac System, Inc.). Self-adhesive Ag-AgCl electrodes (Meditrace 130 ECG conductive adhesive electrodes; Kendall, Inc. Meditrace electrodes, Mansfield, MA, USA) were positioned 2 cm apart (center to center) parallel to the direction of the GM, TA, and SOL muscle fibers on the center of the muscle belly of the dominant leg (22). The ground electrode was placed on the lateral malleolus of the same leg. Before the placement of electrodes, the area of skin was shaved and abraded to remove dead skin with sandpaper and cleansed with an isopropyl alcohol swab to decrease skin resistance. An interelectrode impedance of ,5 kV was obtained before recording to ensure an adequate signal-tonoise ratio. The location of EMG electrodes during the first experimental session was indicated with a permanent marker to ensure the same placement during the second session. Electromyographic signals were filtered with a Blackman VOLUME 30 | NUMBER 2 | FEBRUARY 2016 |

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Compression Effects on Fatigue and Performance Participants were instructed to reduce contact time and jump as high as possible, while keeping their hands on their hips (36). In addition, participants were told to perform drop jumps emphasizing ankle movement, while minimizing movements in the knee and hip. The variables measured were take-off velocity, jump height, contact time, flight time, and peak vertical ground reaction force (GRF). Of the 2 jumps for each drop height, Figure 3. Skin temperature (in degree celsius). zIn the ankle CG condition, skin temperature significantly only the drop jump that increased at post-warm-up and post-fatigue protocol compared with pre-warm-up (p , 0.001). #Skin temperature showed the highest jump at post-warm-up and post-fatigue protocol is significantly increased with ankle CG compared with control height was used for data (p , 0.001). CG = compression garment. analysis. Peak vertical GRF was obtained directly from the force platform data and calculated as 261 dB band-pass filter between 10 and 500 Hz, amplified the peak force produced during the execution of a drop (bipolar differential amplifier, input impedance = 2 MV, jump. Contact time was defined as the time between the first common mode rejection ratio .110 dB minute [50/60 foot contact with the force platform (onset defined as a value Hz], gain 3 1,000; noise ,5 mV), and analog-to-digitally greater than 10 N) and when the participant’s feet left the converted (12 bit) and stored on a personal computer for platform (defined as a value less than 10 N). Flight time was further analysis. Electromyography was analyzed over a 1.5defined as the time between when the participant’s feet left second period (same as force analysis); 0.75 seconds before the force platform and subsequently contacted it again. Jump and after the MVC peak force. Mean rectified root mean height was determined for each drop jump through calculasquare (RMS) EMG was collected and analyzed. The mean tion of take-off velocity (1) using the following formula: amplitude of the EMG RMS was calculated through the software from 50-millisecond bins within 1.5-second window.   flight  time The absolute mean amplitude measures were used for data Take-off   velocity ¼ 9:813 ; 2 analysis. Skin Temperature. Skin temperature was monitored throughout the testing session by taping the temperature sensor (SA1-RTD; Omega Engineering, Inc., Stamford, CT, USA) at the widest point of the calf over the muscle belly of the gastrocnemius lateralis. Skin temperature was measured over a 1-minute period during pre-warm-up, post-warm-up, and post-fatigue protocol and the mean value was calculated and used for the data analysis. Drop Jump Measures. Drop jumps were conducted 10 minutes post-warm-up. All post-warm-up measures were the same as pre-warm-up but with the addition of drop jumps from 20, 35, and 50 cm platform height onto a force plate (400 3 600 3 83 mm, model BP400600 HF-2000; AMTI, Watertown, MA, USA) connected to an amplifier (AMTI Miniamp MSA-6-Gain 2000). All force plate data were collected at 200 Hz. During the familiarization session and before the actual experimental sessions, participants were familiarized with the drop jump technique. There were 2 jumps from each platform height, with 1-minute rest between each jump. To avoid order effect, all drop jumps were randomized.

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Jump  height ¼

ðtake-off   velocityÞ2 : 239:81

Statistical Analyses

Statistical analyses were computed using SPSS software (version 16.0; SPSS, Inc., Chicago, IL, USA). Normality (Shapiro-Wilk) and assumption of sphericity (Mauchley) tests were conducted for all of the dependent variables. If the assumption of sphericity was violated, the GreenhouseGeisser correction was used. First, intraclass correlation coefficients (ICCs) and coefficients of variation (CV) were calculated for mean force, EMG, and evoked muscle contractile properties measured during pre-warm-up to assess consistency across experimental conditions. In addition, paired-samples t-test was used to compare pre-warmup values to make sure there was no significant difference between conditions. Because no significant difference was observed between experimental conditions at pre-warm-up for all dependent variables, absolute values were used for

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mean 6 SD, and in figure as mean 6 SE. Cohen’s d effect sizes (ESs) were also calculated to determine the magnitude of the differences between groups (13). The following criteria were used: negligible (,0.2), small (,0.5), medium (,0.8), and large (.0.8) effect.

RESULTS All participants were able to complete both experimental sessions. The ICCs of the prewarm-up values for MVC force (ICC = 0.89, CV = 0.04 6 Figure 4. Half-relaxation time (milliseconds). †Irrespective of condition, half-relaxation time was significantly decreased at post-warm-up and post-fatigue protocol compared with pre-warm-up (p # 0.05). *A significant main 0.03), EMG gastrocnemius effect for condition was observed (p = 0.043). CG = compression garment. (ICC = 0.84, CV = 0.17 6 0.08), EMG SOL (ICC = 0.88, CV = 0.25 6 0.16), halfrelaxation time (ICC = 0.94, CV = 0.08 6 0.04), rate of further analysis. Second, a 2-way repeated-measure analysis twitch development (ICC = 0.95, CV = 0.05 6 0.02), and of variance (ANOVA) was conducted to determine the effect peak twitch force (ICC = 0.93, CV = 0.18 6 0.16) were all of experimental conditions (CG vs. control) 3 3 time points (pre-warm-up, post-warm-up, post-fatigue protocol) on highly correlated. Paired samples t-test showed that there evoked muscle contractile properties, MVC force, F100, were no significant differences between experimental conditions at pre-warm-up for all variables (all p . 0.4). EMG, skin temperature, and blood lactate values. Third, a 2-way repeated-measures ANOVA was used to determine Skin Temperature the effect of two 2 conditions 3 2 time points (post-warm-up Significant interaction (F(2,28) = 7.54, p = 0.002), condition and post-fatigue protocol) on drop jump performance. Bon(F(1,14) = 15.93, p = 0.001), and time effects (F(2,28) = 17.23, ferroni post hoc tests were used if main effects were found p , 0.001) were found for skin temperature. At the prefor condition or time effects and paired-sample t-tests were warm-up, there was no significant difference between the used if significant interaction of time 3 condition was experimental conditions (p = 0.18); however, skin temperaobserved. Finally, a paired-sample t-test was used to comture was higher in the ankle CG condition, both at the postpare differences between experimental conditions for jumpwarm-up (p , 0.001, ES = 0.9, D4%) and post-fatigue ing TTF. Significance was set at 0.05. Data are reported as protocol (p = 0.001, ES = 0.7, D3.2%). Skin temperature increased from pre- to postwarm-up (p , 0.001, ES = 0.8, D3.5%) and pre-warm-up to post-fatigue protocol in ankle CG condition (p , 0.001, ES = 0.7, D3.4%) (Figure 3). Evoked Muscle Contractile Properties

Figure 5. MVC torque (N$m). †Irrespective of condition, MVC torque significantly decreased compared with post-warm-up (p = 0.029). CG = compression garment; MVC = maximal voluntary contraction.

Although there were no significant condition and time effects for peak twitch force and time to peak twitch (p . 0.05), halfrelaxation time showed significant condition (F(1,14) = 4.93, p = 0.043) and time effects (F(4,56) = 4.22, p = 0.042). Half-relaxation time was

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Compression Effects on Fatigue and Performance was a main effect for time for F100 (F(4,56) = 9.40, p , 0.001), where post-fatigue protocol F100 showed significantly lower values than pre-warmup (p = 0.001, ES = 0.5, D21.2%). There were no significant main effects or interactions for TA or SOL EMG. There was a significant time effect for GM EMG activity (F(4,52) = 3.43, p = 0.015). Gastrocnemius medialis EMG activity decreased significantly at post-fatigue protocol compared with postFigure 6. GRF (N) from 50 cm DJ. #GRF at post-warm-up was significantly greater in the control compared with warm-up (p = 0.05, ES = 0.4, ankle CG condition (p = 0.044). CG = compression garment; DJ = drop jump; GRF = ground reaction force. D12.7%). Similarly, there was a time main effect for SOL EMG (F(4,56) = 7.90, p , significantly shorter during the ankle CG condition com0.001), with significant decrease at post-fatigue protocol pared with control condition (p = 0.043). Regardless of compared with post-warm-up (p # 0.05, ES = 0.3, D11.1%). experimental condition, significantly shorter half-relaxation Ground Reaction Force time was observed for post-warm-up (p = 0.001, ES = 0.4, No interactions or significant main effects were found for the D9.2%) and post-fatigue (p = 0.04, ES = 0.4, D9.0%) comdrop jump variables (p . 0.05), except for a significant interpared with pre-warm-up (Figure 4). action effect for GRF at the 50 cm platform height (F(1,14) = Maximal Voluntary Contraction Force and Electromyography 4.597, p = 0.05). Paired samples t-test showed that the ankle There was a significant main effect for time for MVC force CG condition showed a lower 50-cm GRF at post-warm-up (F(4,56) = 6.052, p , 0.001), but no significant main effect for compared with control (p = 0.044, ES = 0.4, D9.9%); however, condition (p = 0.338) nor interaction of condition 3 time there was no significant difference between conditions at post(p = 0.812). Maximal voluntary contraction force significantly fatigue protocol (p = 0.58). A significant increase was observed declined at post-fatigue protocol compared with post-warmfor 50-cm GRF in the ankle CG condition from post-warm-up up (p = 0.029, ES = 0.2, D8.1%) (Figure 5). Similarly, there to post-fatigue protocol (p = 0.01, ES = 0.4, D12.2%) (Figure 6). Blood Lactate

Figure 7. Blood lactate concentration (in millimoles per liter). †Irrespective of condition, blood lactate values significantly increased at post-warm-up and post-fatigue protocol compared with pre-warm-up (p # 0.05). zIrrespective of condition, blood lactate values significantly increased at post-fatigue protocol compared with postwarm-up (p , 0.001). CG = compression garment.

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Blood lactate during the drop jump TTF did not show any differences between conditions (p = 0.475, ES = 0.16, D11.1%). The blood lactate results demonstrated a significant main effect for time (F(2,28) = 59.17, p , 0.001). Blood lactate values were higher at post-fatigue protocol compared with prewarm-up (p , 0.001, ES = 2.60, D304%) and post-warmup compared to pre-warm-up (p = 0.007, ES = 1.68, D89%), as well as post-fatigue protocol compared with post-warm-up (p , 0.001, D114%) (Figure 7). However, no significant main effect was observed for condition (F(1,14) = 0.019, p = 0.892)

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Journal of Strength and Conditioning Research and interaction of conditions 3 time (F(2,28) = 0.49, p = 0.61). The blood lactate at post-fatigue protocol was 8.61 6 3.44 mmol$L21 for the ankle CG condition vs. 8.10 6 2.50 mmol$L21 for control condition (p = 0.892, ES , 0.15, D6.1%).

DISCUSSION The main outcomes of the study were that skin temperature was higher with ankle CG compared with control and twitch half-relaxation times were positively affected by ankle CG. There were no significant ankle CG-related changes in peak twitch force, time to peak twitch, MVC plantar flexor force, and calf muscle EMG at any time points. Ankle CG was able to reduce peak GRF from the highest drop jump height (50 cm); however, there were no changes between conditions for jump height, take-off velocity, and contact time. Blood lactate values progressively increased from prewarm-up to post-fatigue protocol; however, ankle CG was not able to attenuate this increase. Similarly, ankle CG was not able to affect jumping TTF or enhance recovery. Overall, the results in the present study suggest that below-knee ankle CG generally does not enhance performance or aid in the recovery after the TTF jump protocol; however, it was able to decrease twitch half-relaxation time and reduce GRF from the highest drop jump height. Increased muscle temperature, which correlates with skin temperature (10), can increase performance (40). Studies on CG have shown higher skin temperatures (17,24) and increased performance (20). Although higher skin temperature was recorded with ankle CG over the 10-minute recovery period, plantar flexor MVC, EMG, most evoked muscle contractile properties, and jump measures were not affected. These findings are in contrast to those of Faulkner et al. (20), who showed that keeping muscles warm after the warm-up produced performance increases. Because we did not directly measured muscle temperature, the lack of effect could be explained by the inability of ankle CG to sufficiently increase muscle temperature, a hypothesis supported by the results of Faulkner et al. (20) who found performance enhancement only with CG that had internal heating elements. Increased GRF and thereby joint forces could contribute to acute and chronic tissue damage (35). For the same jump performance (same jump height, contact time, and take-off velocity), ankle CG was able to produce lower GRF from the highest drop jump height (50 cm), thereby indicating higher jump efficiency. To our knowledge, this is the first study that found reductions in GRF while wearing a CG. Ankle CG might have exerted a beneficial effect on SSC due to the garment’s compressive and elastic properties; although the effects were only found for the highest drop jump height, the results might have an important implication in reducing the risk of impact-associated injuries. It is thought that compression clothing provides mechanical support to muscles, which reduces muscle oscillations/vibrations

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(27,39) and possibly muscle damage (27,31). Furthermore, muscle vibrations increase metabolic demand, which might be a rationale for wearing CGs for sports performance (9). Caution should be taken when interpreting these results, since we were unable to restrict movements in the knee and hip joints. More research is needed to explore this potential benefit of wearing ankle CG. This study confirms previous studies that showed no positive effects of CGs on jumping (25) and TTF performance (38). Conversely, other studies found jumping performance improvements while wearing CGs (26,27), indicating CG ergogenic benefits. Moreover, ankle CG was unable to enhance recovery after the fatiguing task as showed by no change in drop jump performance, and plantar flexor force. This is in contrast to findings by Rugg and Sternlicht (39) who showed that CG could enhance recovery after the fatiguing task as showed by an increased countermovement jump performance. The authors suggested that recoil from the fabric might contribute to performance increases in addition to the compression capability (39). Possible explanation for the lack of effect in our study could be due to the different CG used (CG covering the whole leg vs. CG covering only lower leg), fatiguing protocol used (running for 15 minutes with different intensities vs. jumping task to failure), or due to different outcome variables measured (countermovement jump height vs. drop jump height). Ankle CG decreased twitch half-relaxation time. In activities that require fast contraction and relaxation speeds, ankle CG may exert positive effects by increasing the rate of muscle relaxation when lower contraction forces are exerted. The lack of effect of ankle CG on other voluntary rate-related measures, such as F100, jump take-off velocity, and jump height, might be attributed to the much greater forces applied with the voluntary vs. evoked contractions. The ankle CG compression forces were probably not sufficient to positively affect the rate of force development or relaxation associated with voluntary contraction forces (MVC and jump GRF: 1,500 and .4,000 N, respectively), which were many fold greater than evoked twitch forces (average: 200 N). Ankle CG was unable to exert any beneficial effect on time to peak twitch and peak twitch force, which is in accordance with findings by Duffield et al. (17), but in contrast to findings by Miyamoto et al. (33) who showed that CG can attenuate the decrease in peak twitch force thereby enhancing muscle recovery. It has been suggested that CGs can enhance physical performance through stimulation of the various muscle and joint receptors thereby increasing afferent feedback (proprioception). In this study, below-knee ankle CGs were used, which only compress the ankle and calf muscles, thus not impacting the knee and hip joint. Another explanation for the lack of effects in this study could be due to the low pressure exerted by ankle CG (31). Similarly, Miyamoto et al. (33) only found performance benefits with higher compression intensity. Therefore, further studies will need to compare different types of garments on sport performance VOLUME 30 | NUMBER 2 | FEBRUARY 2016 |

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Compression Effects on Fatigue and Performance to delineate what properties of the CG exactly contribute to possible ergogenic benefits. Although there was a significant blood lactate increase following the fatigue protocol, there were no significant differences between conditions. Application of pressure to the skin with CG can improve venous return (3) and muscle oxygenation (2) as well as a redistribution of blood from superficial to the deeper venous system (31). It can be hypothesized that such enhanced blood circulation could more rapidly remove metabolic byproducts leading to lower blood lactate values. Blood lactate has been shown to be lower in people who wore CGs (38). Conversely, other studies have shown that CGs do not affect blood lactate values (19,32). Berry and McMurray (7) have suggested that lower blood lactate values when wearing CG, besides increased blood flow, could be due to lower lactate production or lactate being retained within the muscle. Therefore, further studies are required to investigate the effect of CGs on blood lactate levels. One of the limitations of this study is that EMG and kinematic data of the drop jumps were not analyzed. Although each participant was instructed to jump as high as possible and reduce contact time, we were unable to control for different drop jump strategies. Moreover, muscle activation levels could have changed between conditions for different drop heights and thereby potentially revealing differences in muscle activity between groups. In addition, another limitation of the study is that the participants were not specifically drop-jump trained, thereby limiting the conclusions of this study only to that population. In summary, the results of this study show that ankle CG can decrease twitch half-relaxation times, increase skin temperature, and maintain it over 10 minutes of inactivity; however, this was not associated with MVC force, or 20- and 35-cm drop jump performance benefits. Ankle CG did show increased efficiency from higher drop jump heights by decreasing GRF while keeping other jump parameters the same, thus showing potential benefits for reducing impactrelated injuries. Ankle CG did not affect jumping TTF, recovery, or lactate clearance indicating a lack of ergogenic effect. More research is needed to compare different types of CGs and the CG properties that might contribute to possible performance benefits.

PRACTICAL APPLICATIONS Based on the results of this study, wearing ankle CG is not recommended for enhancement of voluntary isometric force characteristics or drop jump performance from moderate heights (20 and 35 cm). The lower GRF forces found with higher drop jump performance may provide some injury prevention and energy efficiency benefits with sports involving greater jump heights (e.g., basketball, volleyball). The maintenance of increased skin temperature could improve muscle performance in colder environments, especially when a player must remain inactive for a prolonged period before competing (e.g., fourth-line ice hockey player).

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ACKNOWLEDGMENTS The authors thank the participants for their time and effort and Dr. Thamir Alkanani for his technical support. There were no conflicts of interests. Performance Health (Akron OH) provided the compression garments for this study. Two of the authors participate as members of the scientific advisory council for Performance Health. The results of this study do not constitute endorsement of the product by the authors or the National Strength and Conditioning Association.

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