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APPLIED SCIENCES

Acute Warm-up Effects in Submaximal Athletes

An EMG Study of Skilled Violinists

MCCRARY, J. MATT1; HALAKI, MARK2; SORKIN, EVGENY3; ACKERMANN, BRONWEN J1

Author Information
Medicine & Science in Sports & Exercise: February 2016 - Volume 48 - Issue 2 - p 307-315
doi: 10.1249/MSS.0000000000000765

Abstract

Warm-up before the start of physical activity is commonplace in both athletics and the arts, and it is advocated by leading studies for its potential for injury prevention and performance enhancement in both athletic (10) and musical (24) contexts. Recent reviews, however, have demonstrated that warm-up benefits are more nuanced than anecdotal evidence might suggest (6,26). Furthermore, there are no investigations of warm-up effects on submaximal activities outside of steady-state endurance exercise (9). Elite instrumental musicians are submaximal athletes, performing highly repetitive movements with mean HR as high as 72% predicted HR maximum over the course of a performance (20); these physical demands have been recognized by the American College of Sports Medicine’s “Athletes and the Arts” initiative. Daily training of 6–8 h causes a high incidence of overuse injuries—career injury incidence for symphony musicians is reported as high as 81.3% (1). Determining the effects and mechanisms of warm-up in instrumental musicians is a vital first step towards informing whether warm-up fits into evidence-based injury prevention programs for instrumental musicians and other submaximal athletes.

Comprising the largest proportion of most orchestras, violinists are a logical starting place for investigation of warm-up effects in instrumentalists. Study of violinists was further encouraged by a relatively standardized instrumental setup, use of both small and dynamic movements, and prior physiological investigation into violin performance using surface EMG (sEMG) (2,32). This prior sEMG study of violinists has largely focused on bilateral analysis of upper trapezius muscles, with a maximum of eight shoulder, neck, and right arm muscles simultaneously recorded (32). With technological advances allowing simultaneous wireless recording of 16 sEMG channels, more comprehensive analysis of muscle activity involved in arm movements of the shoulder, upper arm, and forearm is now possible. In addition, prior research indicating that core stability reduces injury risk (23) affords particular importance to the inclusion of core musculature in investigations of potential warm-up–related injury prevention mechanisms.

In any performance-related physiological quantification of warm-up effects, measurement of the effect of the intervention on musical performance and subjective experience is essential for obtaining comprehensive measurement of warm-up effects. Regardless of any physiological benefit, absence of concurrent benefit to performance and/or subjective experience is likely to significantly reduce adherence to any intervention (35).

Accordingly, the purpose of this study was to quantify the effects of a variety of warm-ups (cardiovascular, core muscle, and musical) on muscle activity, musical performance, and subjective experience in violinists. sEMG, sound recordings, and survey data were measured during the varied physical demands of violin performances. This tested anecdotal evidence and current pedagogical and health recommendations by recording effects of the three active warm-ups on all three outcomes.

METHODS

Participants

Inclusion criteria were university (either undergraduate or postgraduate) or full-time professional violinists. Participants (n = 55; 15 male, 40 female; 17 professional, 3 postgraduate, 35 undergraduate; age = 28.2 ± 12.3 yr) were recruited from university music schools and professional orchestras in eight cities across Australia and New Zealand. Age did not significantly differ between experimental groups. The protocol was approved by the University of Sydney Human Ethics Committee before study commencement (HREC # 2013/869), and all participants gave written informed consent before participation in this study.

Pretest Power Analysis

Power analysis was performed using the results of a prior sEMG-based investigation of warm-up from sports medical literature that most closely mirrored our study design (36). Pre– and post–warm-up gastrocnemius activity values were used (pre: 123.6 ± 16.83 mV; post: 145.7 ± 17.1 mV), resulting in an effect size (Cohen’s d (12)) = 1.3532. A priori power analysis was conducted in G*Power 3.1 (16) using an independent means test (β = 0.8, α = 0.05); this analysis revealed that eight subjects per group were required to observe specific effects. Given the novel nature of this investigation, additional subjects (n = 12–16 per group) were recruited to maximize statistical power.

Overview of Testing Protocol

All eligible participants were scheduled for a single 2-h research appointment. Participants were instructed to refrain from playing their instrument or exercising for 12 h preceding testing to avoid warm-up effects from these activities. At the beginning of the testing period, participants completed a pretest questionnaire and physical self-assessment. On the basis of responses to the questionnaire and assessment, participants were randomized in a stratified manner into warm-up groups. Surface electrodes and wireless transmitters were applied to 16 muscle sites. Participants performed five short, randomly ordered musical excerpts both before and after their randomly selected warm-up protocol: cardiovascular, core muscle, musical, or inactive control. Ratings of perceived exertion (RPE) were taken after the pre– and post–warm-up performances. During performances of the excerpts, sound and sEMG were recorded. Sound recording data were adjudicated by an expert jury of professional violinists not affiliated with the study, and sEMG data were analyzed by study personnel blinded to participant warm-up condition. After the excerpt performances, participants completed a posttest questionnaire and maximum voluntary contraction (MVC) protocol for all investigated muscles (Fig. 1).

FIGURE 1
FIGURE 1:
Testing protocol flow diagram.

Surface Electromyography

Selection of muscles for sEMG analysis

Focus was placed on the right arm muscles, based on data from Shan et al. (32) indicating that right (bowing) arm movements have the largest amplitudes and velocity during violin performance. For the bowing action, the following muscles were selected for analysis: right biceps brachii, triceps brachii (lateral head), pectoralis major, anterior deltoid, posterior deltoid, upper trapezius, lower trapezius forearm flexors, and forearm extensors. Left trapezius, a common site of tension and injury in violinists (7,28), was also analyzed, as well as six muscles of the core musculature: right and left upper abdominals, right and left lower abdominals, and erector spinae (L1/T12).

Preparation of the skin and placement of electrodes

Before placement of electrodes, the skin was prepared through vigorous rubbing with alcohol and abrasive gel (NuPrep, Aurora, CO) to reduce impedance. Electrodes were placed according to the methodology of SENIAM (31) (right and left upper trapezius, right lower trapezius, right anterior deltoid, right posterior deltoid, right and left erector spinae (L4), right biceps brachii, right triceps brachii (lateral head)), or for muscles for which SENIAM did not make placement recommendations (right forearm flexors, right forearm extensors, right pectoralis major, right and left upper abdominals, right and left lower abdominals), electrode placements were as per Criswell (13). Two Ag/AgCl surface electrodes (Red Dot, 2258, 3M, Sydney, NSW, Australia) were placed 2 cm apart parallel to the muscle fibers of each selected muscle/muscle group. Fixomull hypoallergenic adhesive tape (Smith & Nephew, North Ryde, NSW, Australia) was applied as needed to prevent movement of electrodes during trials. Electrodes were connected to wireless EMG sensors (TELEmyo DTS EMG sensors; Noraxon, Scottsdale, AZ; ∼14 g, 3.4 × 2.4 × 1.4 cm with first-order band pass filter 10–500 Hz, gain of 500, input impedance >100 MΩ, comma mode rejection >100 dB). The signals were transmitted to a 16-bit resolution receiver (Noraxon TELEmyo DTS belt receiver) and saved to a computer at a rate of 1500 Hz using the MR3 software (Version 3.6.20, Noraxon).

Recording of Violin Excerpts

All excerpts were recorded using either a Zoom H4N Handy Portable Digital Recorder (Zoom, Tokyo, Japan) or an iPhone 4 internal microphone (Apple Inc., Cupertino, CA), with the same device used for each participant’s trial. One participant did not consent to audio recording, resulting in audio recordings for n = 54 participants. Audio recordings from the two recording devices were edited using Garage Band software (Apple Inc.) to align the beginning and end of each recording with the start and finish of each excerpt performance. Additionally, care was taken to match overall volume levels, background noise levels, and the mix between the violin performance and metronome across all recordings.

Adjudication of Violin Excerpts

A separate audio file was created for each performance (i.e., pre– and post–warm-up) of each excerpt. These audio files were randomly ordered and sent to two experienced violin performance adjudicators with no affiliation to the study. Duplicate recordings (n = 20) were included to ensure reliability of adjudication. Each separate audio file was adjudicated using a standard violin performance rubric including intonation accuracy, tone clarity, and overall impression (see Document, Supplemental Digital Content 1, full adjudication rubric, http://links.lww.com/MSS/A563). A score out of 6 (half points possible) was given in each of the three adjudication categories for each excerpt performance.

Pretest Questionnaire

The pretest questionnaire was designed to provide background information regarding participant on- and off-instrument warm-up practices and perceptions of the effects of warm-up on sound quality (see Document, Supplemental Digital Content 2, pretest questionnaire, http://links.lww.com/MSS/A564). Data regarding the location, type, duration, and severity of any participant physical symptoms were also obtained using a model developed by Ackermann et al. (3).

Fitness Self-Assessment

A validated fitness self-assessment visual analog scale (VAS) (34) (100-mm scale) was used to assess participant aerobic fitness and muscle strength; VAS data regarding participant flexibility, endurance, and balance were also obtained.

Stratified Randomization

Prior research has shown that pain (18), sex (15), and fitness levels (22) have the potential to significantly affect muscle contraction amplitude and coordination. To control these variables, stratified randomization was used to allocate participants into warm-up groups. Sealed, randomly ordered opaque envelopes containing warm-up group allocations were prepared by a person not associated with the study for each of the eight subject categories detailed in Figure 2.

FIGURE 2
FIGURE 2:
Stratified randomization flow diagram.

Pain group determinations were based on responses to question 5 (presence of current physical symptoms) in the pretest questionnaire: a “yes” response placed participants in the “pain” group, whereas a “no” response placed participants in the “no pain” group. Similarly, the average value of participant responses to the aerobic fitness and muscular strength portions of the fitness self-assessment VAS determined fitness group designations. An average value <50 mm placed participants in the “unfit” group, whereas an average value >50 mm placed participants in the “fit” group.

Violin Excerpts

A series of five musical excerpts [see Video, Supplemental Digital Contents 3–7, recordings of musical excerpts 1–5 (in corresponding order), 41–47 s, 8.6–9.8 MB, http://links.lww.com/MSS/A565, http://links.lww.com/MSS/A566, http://links.lww.com/MSS/A567, http://links.lww.com/MSS/A568, http://links.lww.com/MSS/A569] was selected with the goal of eliciting performance of a range of typical right arm bowing movements. Excerpt duration was kept brief (45–60 s each) to avoid a warm-up effect from the first pre–warm-up performances. A metronome (Tempo, iPhone app, Frozen Ape Pte. Ltd., Singapore, Singapore) was used during each excerpt performance to standardize performance tempos. The performance order of excerpts was randomized for each participant and maintained for both pre– and post–warm-up performances.

Selected excerpts required the following movements:

  1. Forceful right elbow flexion/extension over full range of motion [Fritz Kreisler, Praeludium and Allegro, bars 1–22, crotchet = 108 bpm]
  2. Fast, alternating right shoulder abduction/adduction over full range of motion [Rodolphe Kreutzer, Prelude #7 for Solo Violin, bars 9–26, crotchet = 108 bpm]
  3. Moderate-intensity right elbow flexion/extension over limited range of motion [Charles de Beriot, Variations in d minor, Op. 1, bars 9–24, quaver = 92 bpm]
  4. Sustained, rapid alternating right elbow flexion/extension and right wrist radial/ulnar deviation over a very small range of motion [Joseph-Maurice Ravel, Sonata for Violin and Piano, 1st mvt, rehearsal markings 9–11, quaver = 160 bpm]
  5. Slow, controlled right elbow flexion/extension over full range of motion [Johann Sebastian Bach/Charles Gounod, Ave Maria, bars 5–15, crotchet = 60 bpm]

RPE

RPE, using the Borg scale from 6 to 20 (31), was obtained after the completion of both the pre– and post–warm-up performances of excerpts.

Warm-up Protocols

All warm-ups had a duration of 15 min and were designed to have moderate-intensity activities, with participants instructed to feel they were working “somewhat hard” (RPE = 11–13).

Warm-up protocols were as follows:

  • Cardiovascular—brisk walk in the areas surrounding the test sites.
  • Musical—standard violin warm-up using specific exercises recommended by a violin professor (see Document, Supplemental Digital Content 8, full description of musical warm-up, http://links.lww.com/MSS/A570).
  • Core muscle—eight exercises designed to activate gluteal, abdominal, and shoulder muscles in all three planes of movement. All movements were performed in a slow, controlled fashion to ensure that core muscles were contracted for the duration of the movement. Exercises could be modified to suit individual fitness levels and were performed in the following sequence (see Table, Supplemental Digital Content 9, full description of core muscle warm-up, http://links.lww.com/MSS/A571): dual loading gluteal bridges, single loading gluteal bridge leg marches, leg crossovers, opposite arm/leg extension, dynamic side plank, shoulder “A,” shoulder “T,” shoulder “W,”
  • Control—participants sat quietly in a chair

Posttest Questionnaire

The posttest questionnaire was administered to gauge participant perceptions of the effect of the assigned warm-up on performance and physical symptoms (see Document, Supplemental Digital Content 10, posttest questionnaire, http://links.lww.com/MSS/A572).

MVC

MVC was performed after both the pre– and post–warm-up performances of the excerpts to avoid any warm-up effects resulting from the MVC protocol. In all the tests, participants were instructed to isometrically contract the intended muscle(s) with maximum effort for 3 s against a resistance provided by the same researcher for all participants. Each exercise was repeated three times, separated by a 1-min rest period. The following 13 tests were performed (see Table, Supplemental Digital Content 11, detailed MVC descriptions, http://links.lww.com/MSS/A573):

  • Standardized set of five shoulder exercises (17): resisted shoulder internal rotation at 90° elbow flexion, resisted abduction at 90° abduction, resisted shoulder flexion at 125° flexion, and resisted shoulder extension at 30° abduction
  • Resisted elbow flexion and extension at 90° elbow flexion. Modifications of the protocols of Khan et al. (21) and Staudenmann et al. (33)
  • Resisted wrist flexion and extension at 90° elbow flexion with forearm supported by a table. Adaptation of data from Weerakkody et al. (37)
  • Supine resisted abdominal crunch, supine resisted crossover crunch, and prone resisted back extension (14)

Signal Processing

Signal processing was performed in MATLAB (Version 2014b, The Math Works, Natick, MA). EMG signals were high-pass filtered at 10 Hz (zero lag, 8th Order Butterworth) and rectified, and then the linear envelope was calculated by low-pass filtering at 3 Hz (zero lag, eighth-order Butterworth). All signals were visually inspected before processing by the blinded study personnel; see Figure 3 for a sample raw EMG signal. Using the maximum amplitude recorded for each muscle across all MVC tests, the excerpt EMG signals were then normalized and expressed as %MVC.

FIGURE 3
FIGURE 3:
A sample raw EMG for a typical subject pre (black)– and post (grey)–warm-up in the musical warm-up group for right/left upper trapezius (U Trap), right/left erector spinae (T ES), right/left upper abdominals (U Abdom), right/left lower abdominals (L Abdom), right pectoralis major (Pec), right anterior deltoid (A Delt), right posterior deltoid (P Delt), right lower trapezius (L Trap), right biceps brachii (Bi Br), right middle triceps brachii (M Tri), right wrist flexors (Flexors), and right wrist extensors (Extensors). The vertical lines indicate the vertical scales equivalent to 50mV. The pre- and postsignals are offset from each other for clarity.

Statistical Analysis

All statistical analyses were performed using Statistica 64 version 10 (StatSoft, Inc., Tulsa, OK).

EMG data

The EMG data were checked and confirmed to be normally distributed using probability plots. Pre-/postdifferences in the average EMG levels for different warm-up protocols, excerpts, fitness groups, and pain groups were investigated for each muscle using a three-factor (warm-up protocol × excerpt × pre/post) repeated-measures ANCOVA. When significant main or interaction effects were observed, a Tukey HSD post hoc test was conducted to determine differences among the levels. A significance level α = 0.05 was set.

RPE

Differences in RPE were determined using Wilcoxon matched pairs tests to compare pre-/post-RPE within each warm-up protocol. A significance level α = 0.05 was set.

Sound recording

Differences in perceived performance quality were determined using a two-factor (pre/post × warm-up protocol) repeated-measures ANOVA for each of the three adjudication scores (tone, intonation, overall performance) for each excerpt. When significant main or interaction effects were observed, a Tukey HSD post hoc test was conducted to determine specific significant differences. A significance level α = 0.05 was set.

Trial Registration

This study was prospectively registered with the Australian New Zealand Clinical Trials Registry, ID: ACTRN12614000001695.

RESULTS

Muscle activity: mean activation levels

Average muscle activity levels across ranged from 2.065 ± 0.98 %MVC (right posterior deltoid, excerpt 5) to 55.41 ± 43.76 %MVC (right wrist flexors, excerpt 4). Significant differences in muscle activity levels between excerpts were seen within each investigated muscle (F4,164 ≤ 3.08, P ≤ 0.02) (see Fig. 4).

FIGURE 4
FIGURE 4:
Mean (±SD) muscle activity levels by excerpt. Lower case letters correspond to the following significant differences in muscle activity levels between excerpts: a = 1 versus 2; b = 1 versus 3; c = 1 versus 4; d = 1 versus 5; e = 2 versus 3; f = 2 versus 4; g = 2 versus 5; h = 3 versus 4; i = 3 versus 5; j = 4 versus 5.

Muscle activity: pre- and posteffects

Significant pre-/postdifferences in muscle activity levels were only seen in the right upper trapezius in the musical warm-up group (F3,45 = 4.00, P < 0.02; pre: 6.9 ± 4.2 %MVC; post: 7.6 ± 4.1 %MVC) and right lower trapezius in the core muscle warm-up group (F3,44 = 2.99, P < 0.05; pre: 9.4 ± 6.3 %MVC; post: 8.7 ± 5.7 %MVC). No warm-up–pre-/postinteraction was observed in any of the muscles investigated (F3,45 ≤ 2.18, P ≥ 0.10).

RPE

The RPE significantly decreased for all warm-up groups (Z ≥ 1.99, P < 0.05) except for the control group (Z = 1.18, P > 0.23) (see Fig. 5).

FIGURE 5
FIGURE 5:
RPE, pre– and post–warm-up for each group. *Significant pre-/postdifference (P < 0.05).

Recording adjudication

No significant differences were found in any adjudication scores for any of the groups (F3,45 ≤ 5.43, P ≥ 0.21) (see Fig. 6).

FIGURE 6
FIGURE 6:
Musical performance adjudication scores for each group, pre– and post–warm-up for each excerpt. *Significant pre-/postdifference (P < 0.05).

DISCUSSION

None of the investigated warm-ups significantly impacted musical performance quality or muscle activity levels across all 16 investigated muscles. An acute increase in muscle activity level occurred in the right upper trapezius in the musical warm-up group, and an isolated decrease in muscle activity occurred in the lower trapezius in the core muscle warm-up group; these outlying and contrasting results are likely anomalous. There was, however, a significant decrease in RPE after all warm-up conditions in contrast to no change in RPE after 15 min of silent sitting (control condition).

The presence of significant differences in muscle activity levels between excerpts in all investigated muscles, core and right arm musculature alike, confirms that the variable physical demands of violin performance were successfully captured by the methodology of this investigation. This face validity makes the absence of acute changes in muscle activity levels in response to warm-up in even the most vigorous excerpt even more surprising. However, although these results run contrary to anecdotal evidence and pedagogical recommendations, these results are consistent with the growing body of sports medical evidence suggesting that warm-up is only an effective means of performance enhancement for strength and power outcomes (26). The submaximal sustained muscle activity levels required by violin performance may not be acutely affected by a 15-min warm-up. Warm-ups of varying duration were not investigated and could affect results, although, generally, warm-up durations longer than 10 min have not been shown to have differential effects (9).

The absence of significant musical performance improvements after warm-up also runs contrary to anecdotal evidence but is consistent with previous study (27). In this investigation, 46 of 55 (83.6%) participants anticipated that warm-up would improve performance quality on their pretest questionnaires, whereas outside listeners reported no significant improvements in performance adjudication scores. A similar perceptual divide was also reported in a prior study of vocal performance (27), suggesting that any benefits of warm-up for musical performance may be imperceptible to all except the performers themselves. Likewise, the absence of significant differences between any first and second excerpt performances (e.g., training effect) demonstrates that repetition-based improvements were also imperceptible to trained listeners. This indicates either that a more sensitive measurement tool is necessary to capture performance improvements resulting from warm-up and/or repetition, or that acute performance improvements from both warm-up and repetition in expert violinists are in fact imperceptible even to trained listeners.

An important finding in this investigation is the fact that participants subjectively reported that all three warm-ups significantly decreased performance exertion, in spite of objective muscle activity data to the contrary. The absence of a significant decrease in exertion in the control condition indicates that any warm-up–induced decreases in exertion were not the result of further familiarization with the musical excerpts. Further, the decrease in exertion across all three warm-up protocols, rather than the musical protocol only, suggests that warm-up benefits on exertion are not simply the result of increased time with the instrument before the second excerpt performance. The observed warm-up benefits appear to be the result of other phenomena.

One possible physiological explanation for the decrease in exertion after warm-up is an increased efficiency of oxygen delivery. Prior research demonstrates that muscle temperature rises from resting levels after 3–5 min of activity, reaching equilibrium after 10–20 min of continued activity (30). Associated with this muscle temperature increase is a decreased V˙O2 response time (11), regardless of the intensity of prior warm-up activity (19), due to a decrease in hemoglobin O2 affinity (5), increase in myoglobin O2 affinity (5,29), and increase in total blood flow via vasodilation (4). Whether these physiological changes affect performance of submaximal, repetitive activities has yet to be investigated. Each of the 15-min moderate-intensity warm-up protocols in this investigation may have sufficiently affected such physiological variables to create the observed significant drop in RPE.

An additional, more sparingly investigated hypothesis for participants’ decreased post–warm-up exertion is that warm-up is psychologically beneficial, as it provides time for valuable mental preparation before, in this case, the second performance of the excerpts (8). If this were the case, however, the control condition should have also resulted in decreased exertion, as 15 min of silent sitting affords the same mental preparation time as the three experimental warm-up protocols. Further, prior research has shown, albeit in athletics rather than performing arts, that any positive psychological responses to the completion of a warm-up (e.g., maintenance of preperformance habits) have an insignificant effect on performance (25). As such, it seems unlikely that warm-up benefits are the result of these psychological effects.

A final related hypothesis for the decrease in post–warm-up exertion in the warm-up groups but not the control group is that warm-up has a placebo effect. A large majority of participants (51/55, 92.7%) reported that warm-up was a regular part of their prepractice and performance routines, signifying that most viewed warm-up as a beneficial preparatory activity. Accordingly, the perceived exertion results in the warm-up and control groups could be an extension of previously held attitudes. Conversely, other physiological or psychological factors not considered in this manuscript could also be responsible for these perceived warm-up benefits; further research is necessary.

In summary, this investigation provides some insight into acute warm-up benefits (decreased exertion) that have led to the widespread adoption of this practice for submaximal activities such as musical performance, and it also provides data that refute potential hypotheses regarding the physiological mechanisms behind warm-up benefits in violin performance. Limitations of this study were that sEMG amplitude was the only investigated physiological outcome, a possible placebo effect of warm-up attitudes was not controlled, and the performance quality measurement protocol was potentially not sensitive enough to detect small changes in performance quality. Vascular and V˙O2 responses to warm-up, as well as the warm-up placebo effect, appear to be potentially fruitful avenues for future investigation of warm-up benefits.

CONCLUSION

Cardiovascular, core muscle, and musical warm-up had no acute effect on muscle activity levels or performance quality. RPE was significantly decreased across all three warm-up conditions but not the control condition. This investigation provides data from the performing arts in support of the growing body of sports medical evidence suggesting that warm-up only effectively enhances maximal strength and power performance. Future investigation should focus on elucidating the mechanisms behind subjective warm-up benefits during submaximal activity.

This work was supported by the Australian-American Fulbright Commission and an Australian Research Council Linkage Project Grant (LP0989486).

The authors declare no conflicts of interest. The results of this study do not constitute endorsement by the American College of Sports Medicine.

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Keywords:

PERFORMING ARTS MEDICINE; ATHLETES AND THE ARTS; ELECTROMYOGRAPHY; MUSCLE ACTIVITY

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