Why do the members of one orchestra generally sway while playing, and the others don't?

Question

I'm listening/watching to two videos on YouTube with two different orchestras, each playing a rather distinct style of music, but the members of one really seem to get into the physicality of playing

While the other orchestra's players seem to make no movements other than the ones necessary to play their instruments:

I'm not at all a musician of any kind or have any music training, so can someone explain the playing differences (or maybe explain that there aren't any and I'm not actually seeing something)?

Answer 1

The first orchestra doesn't have a conductor standing in front of them keeping them together. Rather, the keyboardist is conducting, and since his hands are busy, he uses body movement to convey musical instructions, and the rest of the orchestra reciprocates so that it's clear everyone is in sync.

The second orchestra has a conductor dedicated solely to conducting, so the body movement from the orchestra is less necessary.

The size of the orchestras may also play a role. In a large orchestra, there just isn't the kind of room to move. And the role of the conductor has evolved with a rather authoritarian bent, so there's a traditional sense of strict discipline built into many orchestras.

By contrast, the early music ensemble is more spaced out, with some musicians standing. There's greater freedom to move, and since the performance practice has evolved (or, re-evolved) more recently, there is a looseness to it that hasn't made its way into symphony orchestras in the same way.

Answer 2

There are various reasons behind what you're seeing, and most of them are due to the differences between those pieces:

The first example contains a “small” ancient music ensemble. But don't get confused by the concept of “small”: actually, for ancient music, that's rather big, it was only in the last 2 centuries that standard orchestral instrumentation has increased in numbers, with pieces requiring even hundreds of musicians. Up until 1800, orchestras rarely had more than 40 players; in previous centuries it was more common to have small ensembles and chamber music was more popular and performed.

Having a large orchestra also means that large groups of its players play the same thing (unison), especially in strings, while in small ensembles almost all instruments have their own part that is not doubled by any other.

When you're the only one playing your part, you have more “room” for interpretation, and more interpretation often leads to bigger movements, even if they are not directly related to those required for playing. Have a look at this, for example:

As you can see, the soloist is doing a lot of movements.
This is somewhat important for performance, as any body movement has a partial role in the resulting sound and expression. You shouldn't move too much, but you shouldn't stand completely still either.

If you look closely at the second video, you'll see that wind instruments actually move a lot more than string players, and that's also for similar reasons.
Playing the same parts as other musicians also means that you have to “play less” (be aware, this doesn't mean you play less notes or you play with less emphasis).

Another aspect depends on the speed: controlling an instrument demands precision, and playing fast music requires faster control on the instrument, which could be a problem if you move too much.
Also, the type of instrument creates physical differences that allow or require more movements.

There's also other related aspects to consider for the ensamble: when lots of people move in the same way (since they're playing the same thing), the overall perception of movement is less, and the musicians also actually have less physical room – which also means that they shouldn't move too much, or they would distract their colleagues.

Finally, and you can clearly see this by comparing the video above with your first example, playing while standing up (which is common for ancient music ensembles) allows you more freedom of movements.