As recently as 12 months ago a strong thematic which investors were looking to gain exposure to was the strengthening US dollar (USD).

There were a number of ways to play this theme including buying into companies which benefited from the translation benefit from earning US dollars and converting those earnings back into Australian dollars.

Likewise, there was the benefit of exposure to the US economy which appeared to be growing at a stronger rate than the Australian economy, thus providing a better tailwind for US-exposed businesses.

After trading around parity for much of 2011 through early 2013, since May 2013 the Australian dollar (AUD) has weakened against the USD. This set the scene for the US thematic trade.

Since 2013, the US dollar has strengthened significantly, resulting in the Australian dollar buying just US 70 cents – a level which was seen as roughly the “natural” foreign exchange (FX) rate.

Recently however this apparent trend appears to have reversed somewhat with the AUD regaining some strength to trade as high as US 78 cents. Currently the AUD is buying US 74 cents.

Two stocks which have achieved outperformance compared with the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) since May 2013 are ResMed Inc (CHESS) (ASX: RMD) and Brambles Limited (ASX: BXB).

Over the past three years the share price of ResMed has surged around 80%, while shares in Brambles have rallied about 45%. In contrast, the index has gained just 2.5%.

For investors who were shrewd enough to jump aboard this thematic the rewards have been impressive.

The recent strength in the AUD however could be a timely reminder that the best gains from this “trade” are now over.

While there are of course numerous factors to consider when analysing a business and determining whether to sell, a reversal of the foreign exchange currency trend could be a reason for some investors to lock in profits.

What investment theme is set to soar in 2016?

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Motley Fool contributor Tim McArthur has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.